Chemical conversion solution for metal structure and surface treating method

ABSTRACT

The present invention provides a chemical conversion solution and the surface treating method for realizing high corrosion resistance and high coating adhesion of the metal surface, as well as high throwing power during electrodeposition, and generating no sludge. 
     A chemical conversion solution comprising (A) at least one compound selected from water-soluble germanium compound, water-soluble tin compound, and water-soluble copper compound, (B) at least one compound selected from water-soluble titanium compound and water-soluble zirconium compound, (C) at least one water-soluble nitrate compound, (D) at least one compound selected from water-soluble aluminum compound and water-soluble magnesium compound, (E) at least one water-soluble zinc compound, and (F) at least one fluorine compound, and, the coating process for the metal structure.

CROSS-REFERENCE TO RELATED CASES

This application is a continuation under 35 U.S.C. Sections 365(c) and120 of International Application No. PCT/JP2009/061859, filed Jun. 29,2009 and published on Jan. 7, 2010 as WO 10/001,861, which claimspriority from Japanese Patent Application Serial No. 2008-172616 filedJul. 1, 2008, which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

This invention relates to a novel chemical conversion solution for ametal surface, and in particular, for a surface of a metal structurewhich provides excellent corrosion resistance and improved coatingadhesion to the metal surface. This invention also relates to a novelsurface treating method for a metal structure.

Chemical conversion for the purpose of improving the corrosionresistance and coating adhesion of a metal has been known in the art fora long time. The most popular chemical conversion is phosphate treatmentusing an acidic aqueous solution of phosphoric acid. In the case of mostcommon metal material, namely, steel material, surface of the metalmaterial is etched (corroded) when the metal material is brought incontact with the phosphoric acid, and as a consequence of theconsumption of the phosphoric acid, pH increases at the solid-liquidboundary, and this results in the deposition of the insoluble phosphateon the surface of the steel material. By adding zinc, manganese, or thelike to the surface treatment solution, a crystalline salt such as zincphosphate or manganese phosphate can be deposited on the surface. Suchphosphate film is adequate as a primer coating for the subsequentcoating since it has various excellent effects such as improvement ofthe coating adhesion, provision of the resistance to the corrosion underthe coating, and great improvement in the corrosion resistance.

Phosphate treatment itself has been used in the art for almost a hundredyears, and various improvements have been proposed during this period.However, since it etches the steel material, iron dissolves as abyproduct of the chemical conversion reaction. This iron is precipitatedin the reaction system as iron phosphate, and the iron phosphateprecipitate should be periodically discharged from the reaction system.This precipitate is generally called sludge, and at present, this sludgeis either thrown away as an industrial waste or reused as one source forproducing tiles and the like. Recently, reduction of the industrialwaste has become a great agenda in view of global environment, and undersuch situation, the chemical conversion solution and the surfacetreating method which produce no waste is highly demanded.

Chromate chemical conversion is also a popular chemical conversiontreatment. The chromate chemical conversion using chromic acid has longhistory in the industry, and this treatment is still widely used in thesurface treatment of aircraft materials, building materials, andautomobile parts. The chromate chemical conversion solution containschromic acid containing hexavalent chromium as its main component, andtherefore, it forms a chemical conversion film containing hexavalentchromium as its part on the surface of metal material. While thechromate chemical conversion film has excellent corrosion resistance andcoating adhesion, it contains the harmful hexavalent chromium, andaccordingly, there is a strong demands for a chemical conversionsolution and a chemical conversion film free from the environmentallyharmful hexavalent chromium.

In the meanwhile, the metal structure of a transportation vehicle suchas an automobile is subjected to electrodeposition to impartanti-corrosive property with the material. In this case, it has beenglobal practice to conduct the electrodeposition after the chemicalconversion of the metal structure without drying. Electrodeposition is amethod which is capable of forming a relatively consistent coatinghaving uniform coating thickness since the electrodeposition paint isdeposited through electrolysis, and this method is well adapted forcoating various structures. However, in the case of a structure having acomplicated shape as in the case of an automobile body or its part,amount of the electric current will be less in some parts because of thestructure, and in the case of a structure having a pocket structure,coating thickness will be different in the exterior and interiorsurfaces. The ability of forming a consistent coating is generallycalled throwing power during the electrodeposition, and a solution and amethod realizing a high throwing power during the electrodeposition isawaited.

Various inventions have been proposed for the improvement of throwingpower during the electrodeposition.

For example, JP 2004-083824 A discloses a method for forming a coatingby electrodeposition. This method uses a coating composition forcationic electrodeposition containing a base resin comprising analkylphenol and an amine adduct epoxy resin (I) modified withpolycaprolactone, and a curing component comprising blockedpolyisocyanate curing agent (II), and the electrodeposition is conductedunder the conditions wherein polarization resistance (a) per unitcoating thickness of the coating during the electrodeposition of thesubject to be coated having a pocket structure is 125 to 150 kΩ·2cm²/μm, and coating weight (b) per unit electricity is 28 to 50 mg/C tothereby form a coating wherein the throwing power represented by theratio of exterior and interior coating thickness (c) is such that theinterior coating thickness is 10 μm and the exterior coating thicknessis 10 to 12 μm, with the ratio of the interior coating thickness to theexterior coating thickness being 10/10 to 12. JP 2004-083824 A alsodiscloses a coating composition for cationic electrodeposition for usewith this method and an article coated by this method.

JP 2004-269942 A discloses a method for improving the throwing power inthe cationic electrodeposition wherein the electrodeposition is carriedout by using an electrodeposition paint and adjusting coating propertiesduring the electrodeposition to the following parameters:

(a) electric conductivity of the electrodeposition paint of at least0.16 S/m,

(b) electric conductivity of the coating of up to 1.0×10⁻⁷ S/m,

(c) electricity not contributing for the deposition of up to 320coulomb/m², and

(d) electrochemical equivalence of at least 1.0×10⁻⁴ kg/coulomb,

As described above, insufficient throwing power during theelectrodeposition has been a serious problem in the case of complicatedstructure such as automobile body. However, conventional approach forsolving this problem has been exclusively from the side of the coatingsuch as improvement of the electrodeposition paint and improvement ofthe electrodeposition conditions. Use of the phosphate generallyrealized a relatively high throwing power during the electrodeposition,and in employing an alternative technique, it would be important torealize a throwing power during the electrodeposition equivalent to orhigher than the throwing power realized by the phosphate, andpreferably, improvement of the throwing power by the approach from sideof the surface treatment, namely, from the side of the chemicalconversion film is desired.

Besides the phosphate treatment, numerous chemical conversion solutionsand surface treating methods not using the hexavalent chromium have beenproposed. Not many, however, have been used in the commercialproduction. Some of these inventions are described in the following.

A typical example of the non-chromate type chemical conversion solutioncontaining no chromium at all is the chemical conversion solutiondisclosed in JP 52-131937 A. This chemical conversion solution is anacidic coating composition having a pH of about 1.5 to 4.0 containingzirconium, titanium, or its mixture with phosphoric acid and a fluoride.When a metal surface is treated with this chemical conversion solution,a chemical conversion film containing oxide of zirconium or titanium asits main component is formed on the metal surface. This non-chromatetype chemical conversion solution has the merit that it does not containthe hexavalent chromium, and it has been widely employed in producingaluminum D & I cans for beer and other beverages. This is a classicaltechnique which falls within the category of non-chromium chemicalconversion solution commonly referred to as the “zirconium or titaniumnon-chromium chemical conversion solution”.

The treatment method disclosed in JP 57-41376A is a surface treatingmethod wherein a surface of aluminum, magnesium, or an alloy thereof istreated with an aqueous solution containing at least one member selectedfrom titanium salt and zirconium salt, at least one member selected fromimidazole derivatives, and an oxidizing agent such as nitric acid,hydrogen peroxide, or potassium permanganate. The oxidizing agentpromotes deposition of the titanium or zirconium. This solution iswithin the category of non-chromium chemical conversion solution called“zirconium or titanium solution.

Further examples of the non-chromate type treating solution are thefollowing solutions.

JP 56-136978A discloses a chemical conversion solution comprising anaqueous solution containing vanadium compound and at least one compoundselected from the group consisting of titanium salt, zirconium salt, andzinc salt. This solution is a combination of the zirconium or thetitanium non-chromium chemical conversion solution as mentioned abovewith the vanadium.

JP 2000-199077A discloses an acidic metal surface treating solutioncontaining a metal acetylacetonate and at least one compound selectedfrom water-soluble inorganic titanium compound and water-solubleinorganic zirconium compound. The metal acetate used in this solution isvanadyl acetate, zirconium acetate, zinc acetate, or the like, and thissolution is a combination of the zirconium or the titanium non-chromiumchemical conversion solution as mentioned above with the metal acetate.

JP 11-36082A proposes a surface treating solution for a light metal or alight alloy material comprising 0.01 to 50 g/l of permanganic acid orits salt and 0.01 to 20 g/l of at least one compound selected fromwater-soluble titanium compound and water-soluble zirconium compound,and which has a pH of 1.0 to 7.0. This solution is within the categoryof non-chromium chemical conversion solution called manganese-titaniumor manganese-zirconium solution.

JP 2004-232047A discloses a chemical conversion agent for forming ahighly corrosion resistant chromium-free film adapted for use withaluminum or an aluminum alloy, comprising hexacyano acid ion and atleast one metal ion selected from the group consisting of Ti, V, Mn, Fe,Co, Zr, Mo, and W. The elements indicated other than cobalt are thosementioned in the prior art document as mentioned above.

JP 2001-247977A proposes a chromium-free composition for metal surfacetreatment wherein the film formed by the metal surface treatmentcontains a plurality of metal elements at least one of which ismulti-valent. More specifically, in this metal surface treatingcomposition, at least two members selected from Mg, Al, Ti, V, Mn, Fe,Co, Ni, Cu, Zn, Sr, Nb, Y, Zr, Mo, In, Sn, Ta, and W are used for themetal element. This composition can be understood as a scope withinzirconium, titanium, vanadium, tungsten, molybdenum, or manganesenon-chromium chemical conversion solution.

WO 03/074761A1 proposes a surface treating composition for aluminum, analuminum alloy, magnesium, or a magnesium alloy containing (1) compoundA containing at least one metal element selected from Hf(IV), Ti(IV),and Zr(IV), (2) a fluorine-containing compound at an amount sufficientfor the presence of fluoride at a concentration 5 times higher than thetotal molar concentration of the metal in the compound A, (3) at leastone metal ion B selected from alkaline earth metal, (4) at least onemetal ion C selected from Al, Zn, Mg, Mn, and Cu, and (5) nitrate ion.In broad sense, this solution is also a scope within the zirconium ortitanium non-chromium chemical conversion solution.

JP 2003-313679A proposes a non-chromium metal surface treating methodcomprising the steps of (A) treating the subject to be treated with anon-chromium metal surface treating agent comprising a water-solublezirconium compound and/or a water-soluble titanium compound (1) and anorganic phosphonic acid compound (2); and (B) treating the subject whichhad been treated by the step (A) with an aqueous solution of tannin (3);wherein content of the water-soluble zirconium compound and/or thewater-soluble titanium compound (1) is 40 to 1000 ppm by weight in termsof the amount of the zirconium and/or titanium, content of the organicphosphonic acid compound (2) is 20 to 500 ppm by weight, and thenon-chromium metal surface treating solution has a pH of 1.6 to 4.0, andcontent of the tannin (3) in the aqueous solution is 400 to 10000 ppm byweight. In broad sense, this solution is also a scope within thezirconium or titanium non-chromium chemical conversion solution.

JP 2003-313681A proposes a non-chromium metal surface treating methodcomprising the steps of (A) treating the subject to be treated with anon-chromium metal surface treating agent comprising a water-solublezirconium compound and/or a water-soluble titanium compound (1) and anorganic phosphonic acid compound (2); and (B) treating the subject whichhad been treated by the step (A) with an aqueous solution of tannin (3);wherein the organic phosphonic acid compound (2) is a compound whereinthe phosphorus atom constituting the phosphonic group is bonded tocarbon atom, content of the water-soluble zirconium compound and/or thewater-soluble titanium compound (1) is 20 to 800 ppm by weight in termsof the amount of the zirconium and/or titanium, content of the organicphosphonic acid compound (2) is 10 to 500 ppm by weight, the aqueoussolution of tannin (3) has a concentration of 300 to 8000 ppm by weight,and the non-chromium metal surface treating solution has a pH of 1.6 to4.0, and the solution is used for the production of a metal platecovered by a thermoplastic polyester resin. As the prior art documentsas mentioned above, in broad sense, this solution is also a scope withina zirconium or titanium non-chromium chemical conversion solution.

JP 2003-171778A discloses a treating solution which is an aqueous acidicliquid composition containing (A) at least one member selected from thegroup consisting of Ti, V, Mn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, and W, (B)at least one member selected from an organic acid and/or an inorganicacid and/or a salt thereof, and (C) fluorine as an optional component,wherein the aqueous acidic liquid composition contains at least onemember selected from trivalent chromium, Ti, V, Mn, Y, Zr, Nb, Mo, Tc,Ru, Rh, Pd, W, Li, Na, K, Be, Mg, Ca, Al, Fe, Ni, Co, Si, Sr, In, Ag,Zn, Cu, Sc, organic acid, inorganic acid, organic acid salt, inorganicacid salt, amino acid, amino acid salt, fluorine, amine, alcohol,water-soluble polymer, surfactant, silane coupling agent, carbon powder,dye, pigment, organic colloid, and inorganic colloid. As the prior artdocuments as mentioned above, this solution is a scope within azirconium and/or titanium non-chromium chemical conversion solution.

JP 2004-218070A discloses a pretreatment method to be conducted beforethe coating comprising the step of treating the subject to be treatedwith a chemical conversion solution to form a chemical conversion film,wherein the chemical conversion solution contains at least one memberselected from zirconium, titanium, and hafnium; fluorine; and at leastone member selected from amino group-containing silane coupling agentand its hydrolysate and polymerization products thereof. As in the caseof the prior art documents as mentioned above, this solution is a scopewithin a zirconium and/or titanium non-chromium chemical conversionsolution, and this solution also includes a silane coupling agent whichis known in the art.

JP 2004-218073A proposes a chemical conversion solution comprising atleast one member selected from zirconium, titanium, and hafnium;fluorine; and an agent for improving adhesion and corrosion resistance,wherein the agent for improving adhesion and corrosion resistance is atleast one member selected from the group consisting of 1 to 5000 ppm (interms of the metal ion concentration) of at least one metal ion (A)selected from zinc, manganese, and cobalt ions; 1 to 5000 ppm (in termsof the metal ion concentration) of an alkaline earth metal ion (B); 1 to1000 ppm (in terms of the metal ion concentration) of a Group III metalion (C); 0.5 to 100 ppm (in terms of the metal ion concentration) ofcopper ion (D); and 1 to 5000 ppm (in terms of the silicon component) ofa silicon-containing compound (E). As in the case of the prior artdocuments as mentioned above, this solution is a scope within azirconium and/or titanium non-chromium chemical conversion solution, andthis solution also includes components such as zinc ion or the like,alkaline earth metal ion, Group III metal ion (which is described to bepreferably aluminum), copper ion or the like, and silicon-containingcompound as the an agent for improving adhesion.

JP 2004-218075A proposes a chemical conversion solution comprising atleast one member selected from zirconium, titanium, and hafnium;fluorine; an agent for improving adhesion; and an agent for promotingthe chemical conversion reaction, wherein the agent for improvingadhesion is at least one member selected from a metal ion such as zinc,a silicon-containing compound, a water-soluble resin having amino groupand at least having —(—CH₂—CHNH₂—)— or —(—CH₂—CHCH₂NH₂—)— as aconstitutional unit, epoxy compound, and silane coupling agent; and theagent for promoting the chemical conversion reaction is at least onemember selected from the group consisting of nitrous ion, nitrogroup-containing compound, organic acid, and the like incorporated at anamount of 1 to 5000 ppm. As the prior art documents as mentioned above,this solution is a scope within a zirconium and/or titanium non-chromiumchemical conversion solution. However, this solution also includes anorganic compound, and in this sense, this solution is more relevant withthe resin and metal non-chromium chemical conversion solutions asdescribed below.

In the meanwhile, JP 61-91369A, JP 1-172406A, JP 1-177379A, JP1-177380A, JP 2-608A, JP 2-609A, and JP 2771110 B disclose chemicalconversion solutions and chemical conversion methods which involve useof a water-soluble resin for the purpose of providing corrosionresistance and coating adhesion with an aluminum-containing metalmaterial or the like. In these conventional chemical conversionsolutions and chemical conversion methods, the metal surface is treatedby a solution containing a derivative of a polyhydric phenol compound,and these fall within the category called resin or resin metal compositenon-chromium chemical conversion solutions.

JP 2001-303267A proposes a non-chromium chemical conversionrust-preventive solution for aluminum containing a zirconium compound,fluorine ion, a water-soluble resin, and an aluminum salt, wherein thezirconium compound is included at a concentration in terms of thezirconium ion of 100 to 100000 ppm, the fluorine ion is included at aconcentration of 125 to 125000 ppm, the water-soluble resin is includedat 100 to 100000 ppm in terms of the concentration of the non-volatilecontent, and the aluminum salt is included at a concentration in termsof the aluminum ion of 10 to 10000 ppm. This solution is also anon-chromium chemical conversion solution which is a combination of theresin and the zirconium solutions.

Chemical conversion solutions which are not totally free from chromiumbut the one containing not the harmful hexavalent chromium but trivalentchromium have also been proposed. JP 3333611B proposes a hexavalentchromium-free chemical conversion solution for aluminum and aluminumalloys containing acid ion (A) containing a phosphor-containing acidgroup, at least one ion (B) selected from trivalent chromium ion and ionof a compound containing the trivalent chromium, and at least onefluorine compound (C) selected from fluoride and complex fluoride. Thissolution falls within the category of trivalent chromium chemicalconversion solution.

JP 2000-332575A proposes a chemical conversion solution which is usedafter treating a substrate comprising aluminum or an aluminum alloy withan acidic aqueous solution at 10 to 70° C. for 5 seconds to 5 minutes,wherein the acidic aqueous solution is an acidic aqueous solution at apH of up to 2 containing (a) at least one member selected from the groupconsisting of a salt or an acid salt of a metal selected from Fe, Ni,Co, Mo, and Ce at a concentration in the acidic aqueous solution of 0.01to 5% by weight, (b) an inorganic acid; and the chemical conversionsolution comprises (c) Zr and/or Ti at a concentration in the chemicalconversion solution of 0.001 to 1% by mass, (d) trivalent chromium ionor its salt at a concentration in the chemical conversion solution of0.1 to 1000 ppm, and (e) a fluoride. As in the case of JP 3333611 B,this solution also falls within the category of the trivalent chromiumchemical conversion solution.

JP 2004-010937A proposes a method for forming a colored rust-preventivefilm on a metal in which a rust-preventive film is formed by using aliquid composition containing (A) trivalent chromium ion, (B) at leastone member selected from Mo, W, Ti, Zr, Mn, Tc, Fe, Ru, Co, alkalineearth metal, Ni, Pd, Pt, Sc, Y, V, Nb, Ta, Cu, Ag, and Au, (C) at leastone member selected from chlorine, fluorine, sulfate ion, and nitrateion, and (D) at least one member selected from oxyacid, oxysalt, andanhydride of phosphor and phosphorus compound. As in the case of JP3333611B, this invention also falls within the category of the trivalentchromium chemical conversion solution.

JP 2004-3019A proposes a method for forming a chemical conversion filmfree from hexavalent chromium by treating the metal surface with asolution of at least one trivalent chromium chelate complex, wherein thesolution contains trivalent chromium of the chelate complex at aconcentration of 5 to 100 g/l, and the trivalent chromium chelatecomplex has a ligand replacement speed faster than the fluoridereplacement speed in the trivalent chromium-fluoro complex. Thissolution also falls within the category of the trivalent chromiumchemical conversion solution.

Similar technology is often used in zinc die cast. JP 3597542B proposesformation of a substantially coherent conversion film containingtrivalent chromium but no hexavalent chromium on zinc or a zinc alloy,which presents, even in the absence of further components such assilicate, cerium, aluminum and borate, a corrosion protection of about100 to 1000 hours in the salt spray test according to DIN 50021 SS orASTM B 117-73 until first erosion according to DIN 50961 Chapter 10;which is clear, transparent and substantially colorless presentingmulti-colored iridescence; which has a layer thickness of about 100 nmto 1000 nm; which is hard and highly adhesive; and which is resistant towiping. This solution also falls within the category of the trivalentchromium chemical conversion solution.

JP 3784400B by the same inventor as the present invention proposesformation of a chemical conversion film containing 0.02 to 1 mmol/m² ofCr and 0.02 to 1 mmol/m² of Ti and/or Zr and having a thickness of 1 to100 nm, by contacting an aqueous acidic chemical conversion solutionadjusted to a pH in the range of 2.3 to 5.0 containing a water-solubletrivalent chromium compound (A), a water-soluble Ti and/or zirconiumcompound (B), a water-soluble nitric acid compound (C), a water-solublealuminum compound (D), and a fluorine compound (E) with the surface of am al material for 1 to 60 seconds; rinsing with water; and drying tothereby form the film. This solution also falls within the category ofthe trivalent chromium chemical conversion solution.

JP 5-195244A discloses a method for forming a protective film on a metalsurface comprising the step of (I) coating the metal surface with alayer of an aqueous acidic liquid composition, and (II) drying the layerof the aqueous acidic liquid composition without intermediate washing.In this method, the aqueous acidic liquid composition contains water;(A) anion components each comprising (i) at least four fluorine atomsand (ii) at least one element selected from the group consisting oftitanium, zirconium, hafnium, silicon, and boron, and optionally (iii)anion component containing at least one oxygen atom; (B) cationcomponent selected from the group consisting of cobalt, magnesium,manganese, zinc, nickel, tin, zirconium, iron, aluminum, and copper; (C)a free acid of the amount sufficient for maintaining the pH of thecomposition to the range of about 0.5 to about 5.0; and optionally, (D)a component which forms an organic thin layer by direct drying; and thenumber of cations in (B) is at least ⅓ of the number of the anions in(A). This is a dry-in-place type surface treatment method which is atechnology different from the chemical conversion method wherein thefilm is formed by dissolution of the matrix.

JP 2004-238716 A discloses formation of a film having a thickness of0.01 to 5 μm on a zinc, zinc alloy, aluminum, or aluminum alloy platedsteel plate by a surface treatment comprising the steps of coating anddrying a surface treating composition comprising (a) an aqueous epoxyresin dispersion comprising water dispersion of a modified epoxy resinobtained by reacting an epoxy group-containing resin (A), a primaryamine compound and/or a secondary amine compound (B), and an activehydrogen-containing compound (C) partly or entirely comprising an activehydrogen-containing hydrazine derivative, (b) a water dispersion ofurethane resin, (c) a silane coupling agent, and (d) phosphoric acidand/or hexafluorometallic acid. This method is also a coating surfacetreatment.

These conventional proposals on the surface treatment may be categorizedinto (1) use of a zirconium or titanium solution, and their derivativetechniques, (2) use of the solution containing vanadium, molybdenum,tungsten, and cobalt, (3) use of an organic solution containing tannicacid or a water-soluble resin, (4) use of an organic/inorganic compositesolution containing zirconium in combination with a resin, (5) use of atrivalent chromium solution, and (6) dry-in-place type treatment.

Of these proposals, the use of the trivalent chromium solution (5) willleave trivalent chromium in the resulting film, and when this film isexposed to a high temperature, the trivalent chromium will turn into thehexavalent chromium which is harmful to the human body. Accordingly,this technique is inadequate in environmental point of view. Thedry-in-place type treatment (6) can be used for a simple structure as inthe case of a sheet or coil material. However, this surface treatment(6) is unable to form a consistent film when used for a complicatedstructure as in the case of an automobile body due to the formation ofthe liquid pool.

The zirconium solution (1) has sufficient performance for theapplication such as priming for further coating, cold rolled aluminummaterial having consistent surface, and other applications withoutsevere requirement for the corrosion resistance, and some are actuallyused in industrial scale production. For example, the surface treatingsolution of JP 52-131937A containing phosphoric acid, fluorozirconicacid, and nitric acid for the main components is commercially used inthe surface treatment of aluminum D & I cans, and it has been used formore than 25 years. However, in the case of metal structure oftransportation vehicle such as automobile, numerous high levelrequirements are imposed on the chemical conversion process. Forexample, these metal structures have complicated shape and they compriseplurality of different materials such as cold rolled steel plate andzinc-plated steel plate, and it should also enable the subsequentelectrodeposition to be carried out at a high throwing power withreduced amount of the waste from the chemical conversion process. Theserequirements are not fully overcome.

The solution containing vanadium, molybdenum, tungsten, and cobalt (2)is used in the industry. However, this solution does not dramaticallyimprove the corrosion resistance, and as in the case of other solutionsas described above, throwing power during the electrodeposition is notsufficient when used for transportation vehicles such as automobile.

In some cases, corrosion resistance is improved by the use of an organicsolution containing tannic acid or a water-soluble resin (3) or by theuse of an organic/inorganic composite solution (4) containing zirconiumin combination with a resin compared to the use of a zirconium solution(1). However, these solutions are far from perfect in terms of thethrowing power during the electrodeposition in the case of the metalstructure of transportation vehicles such as automobile.

More recently, JP 2008-88551A discloses a metal surface treating methodfor forming an anti-corrosive film on a metal substrate having aplurality of bent portions at high throwing power. This method uses ametal surface treating composition for pretreatment of the cationicelectrodeposition, and this composition contains zirconium ion and/ortitanium ion, an agent for improving adhesion, and a stabilizer forsuppressing dissolution of the components in the anti-corrosive filmduring the cationic electrodeposition, and the agent for improvingadhesion contains at least one member selected from the group consistingof (A) a silicon-containing compound, (B) a metal ion for improvingadhesion, and (C) a resin for improving adhesion. The silicon-containingcompound (A) is at least one member selected from the group consistingof silica, silicofluoride, water-soluble silicate compound, silicateester, alkylsilicate, and silane coupling agent, and the metal ion forimproving adhesion (B) is at least one metal ion selected from the groupconsisting of magnesium, zinc, calcium, aluminum, gallium, indium,copper, iron, manganese, nickel, cobalt, and silver, and the resin forimproving adhesion (C) is at least one member selected from polyaminecompound, blocked isocyanate compound, and melamine resin. When the filmproduced by the example of JP 2008-88551A was compared with theconventional phosphate film, the results were not necessarilysatisfactory.

JP 2008-88552A discloses a surface treating method for improvingthrowing power during cationic electrodeposition, comprising the metalsurface treating step of contacting a metal substrate with a metalsurface treating composition comprising zirconium ion and/or titaniumion and at least one agent for improving adhesion selected from thegroup consisting of (A) a silicon-containing compound, (B) a metal ionfor improving adhesion, and (C) a resin for improving adhesion; and apost treatment step wherein the surface treated metal substrate issubjected to a heat treatment which is at least one treatment selectedfrom the group consisting of (1) the step of drying the metal substrateat a temperature of at least 60° C. and up to 190° C. at atmospheric orhigher pressure for at least 30 seconds, and (2) heating the metalsubstrate in hot water at a temperature of at least 60° C. and up to120° C. at atmospheric or higher pressure for at least 2 seconds and upto 600 seconds. This invention, however, includes a step requiring hotair heater or hot water, and when carried out in commercial scale, itleads to an unfavorable increase in the cost and complication. Hence,this method is not practical.

JP 2008-88553A discloses a metal surface treating method for improvingthrowing power during cationic electrodeposition comprising the stepwherein the metal surface is treated for forming an anti-corrosive filmby using a metal surface treating composition comprising zirconium ionand/or titanium ion and at least one agent for improving adhesionselected from the group consisting of (A) a silicon-containing compound,(B) a metal ion for improving adhesion, and (C) a resin for improvingadhesion; and a post treatment step which is at least one treatmentselected from the group consisting of step (a), step (b), step (c), step(d), step (e), step (f), and step (g). The step (a) is a step in whichthe entire metal substrate which has finished the surface treating stepor a part thereof is brought in contact with an alkaline aqueoussolution at a pH of 9 or more. The step (b) is a step in which theentire metal substrate which has finished the surface treating step or apart thereof is brought in contact with an aqueous solution of apolyhydric anion. The step (c) is a step in which the entire metalsubstrate which has finished the surface treating step or a part thereofis brought in contact with an aqueous solution of a polyhydric anion,and then rinsed with water. The step (d) is a step in which the entiremetal substrate which has finished the surface treating step or a partthereof is brought in contact with an oxidizing agent. The step (e) is astep in which the entire metal substrate which has finished the surfacetreating step or a part thereof is brought in contact with an oxidizingagent, and then rinsed with water. The step (f) is a step in which theentire metal substrate which has finished the surface treating step or apart thereof is brought in contact with a fluorine stabilizer. The step(g) is a step in which the entire metal substrate which has finished thesurface treating step or a part thereof is brought in contact with afluorine stabilizer, and then rinsed with water. This invention,however, requires a post treatment after the chemical conversion, andwhen carried out in commercial scale, it leads to an unfavorableincrease in the cost and complication. Hence, this method is notpractical.

As described above, the chemical conversion film formed by applyingconventional non-chromate type surface treating solution to thetransportation vehicle metal structure such as a automobile metalstructure had various problems such as the insufficient corrosionresistance and coating adhesion. More specifically, there is no chemicalconversion solution or surface treating (surface priming) method whichis capable of realizing the throwing power during the electrodepositionat the level required in the case of an automobile metal structure bysimple steps at reduced cost, and improvement of the throwing powerduring the electrodeposition has been a serious agenda that needsimprovement.

-   Patent Document 1: JP 2004-083824 A-   Patent Document 2: JP 2004-269942 A-   Patent Document 3: JP 52-131937 A-   Patent Document 4: JP 57-41376 A-   Patent Document 5: JP 56-136978 A-   Patent Document 6: JP 2000-199077 A-   Patent Document 7: JP 11-36082 A-   Patent Document 8: JP 2004-232047 A-   Patent Document 9: JP 2001-247977 A-   Patent Document 10: WO 03/074761 A1-   Patent Document 11: JP 2003-313679 A-   Patent Document 12: JP 2003-313681 A-   Patent Document 13: JP 2003-171778 A-   Patent Document 14: JP 2004-218070 A-   Patent Document 15: JP 2004-218073 A-   Patent Document 16: JP 2004-218075 A-   Patent Document 17: JP 61-91369 A-   Patent Document 18: JP 1-172406 A-   Patent Document 19: JP 1-177379 A-   Patent Document 20: JP 1-177380 A-   Patent Document 21: JP 2-608 A-   Patent Document 22: JP 2-609 A-   Patent Document 23: JP 2771110 B-   Patent Document 24: JP 2001-303267 A-   Patent Document 25: JP 3333611 B-   Patent Document 26: JP 2000-332575 A-   Patent Document 27: JP 2004-010937 A-   Patent Document 28: JP 2004-3019 A-   Patent Document 29: JP 3597542 B-   Patent Document 30: JP 3784400 B-   Patent Document 31: JP 5-195244 A-   Patent Document 32: JP 2004-238716 A-   Patent Document 33: JP 52-131937 A-   Patent Document 34: JP 2008-88551 A-   Patent Document 35: JP 2008-88552 A-   Patent Document 36: JP 2008-88553 A

SUMMARY OF THE INVENTION

The present invention is an attempt to solve the problems of the priorart as described above, and in particular, the present inventionprovides a chemical conversion solution and the surface treating methodfor realizing high corrosion resistance and high coating adhesion of themetal surface, as well as high throwing power during electrodeposition.More specifically, the present invention provides a chemical conversionsolution and a surface treating method for a metal structure which iscapable of realizing high throwing power during the electrodeposition ofthe level equal to or higher than the case using a phosphate withoutdrying the pretreated metal structure particularly when applied to anautomobile body or its part, which provides adequate corrosionresistance and coating adhesion to the metal structure, which is alsocapable of controlling and reducing the industrial wastes such as sludgein the commercial scale production, and which is economical andinexpensive.

The inventors of the present invention made an extensive investigationon the measures to solve the problems of the prior art as describedabove, and found that throwing power during the electrodeposition can begreatly improved by depositing a germanium compound, a tin compoundand/or a copper compound on the surface of the metal structure, and as aconsequence, arrived at a new finding that the throwing power during theelectrodeposition can be controlled by means of the underlying film. Theinventors of the present invention also found that an even highercorrosion resistance and coating adhesion can be realized when thegermanium compound, the tin compound and/or the copper compound isdeposited on the metal structure simultaneously with the conventionaltitanium compound and/or zirconium compound to form a composite film.The present invention has been completed on the bases of such findings.

To achieve the above objectives, the present invention provides; Achemical conversion solution for a metal structure comprising

(A) at least one compound selected from water-soluble germaniumcompound, water-soluble tin compound, and water-soluble copper compound

(B) at least one compound selected from water-soluble titanium compoundand water-soluble zirconium compound,

(C) at least one water-soluble nitrate compound,

(D) at least one compound selected from water-soluble aluminum compoundand water-soluble magnesium compound,

(E) at least one water-soluble zinc compound, and

(F) at least one fluorine compound, wherein

content (C_(A)) of at least one member selected from germanium, tin, andcopper is 0.05 mmol/L to 10 mmol/L,

content (C_(B)) of titanium and/or zirconium is 0.1 mmol/L to 10 mmol/L,

content (C_(C)) of nitrate radical in the water-soluble nitrate compound(C) is 3 mmol/L to 300 mmol/L,

content (C_(D)) of aluminum and/or magnesium is 1 mmol/L to 200 mmol/L,

content (C_(E)) of zinc is 0.2 mmol/L to 20 mmol/L,

content (C_(F)) of fluorine in the fluorine compound (F) satisfies thefollowing equations:

C _(F) (minimum value)=C _(A)×2+C _(B)×4+C _(D)×2

C _(F) (maximum value)=C _(A)×4+C _(B)×7+C _(D)×4, and

pH of the chemical conversion solution has been adjusted to the range of2.5 to 4.4.

More preferably, the present invention provides; The chemical conversionsolution for a metal structure wherein the chemical conversion solutionfurther comprises a cationic water-soluble resin (G).

More preferably, the present invention provides; The chemical conversionsolution for a metal structure wherein the chemical conversion solutionfurther comprises a coupling agent (H).

More preferably, the present invention provides; The chemical conversionsolution for a metal structure wherein the chemical conversion solutionfurther comprises a metal chelating agent (I).

More preferably, the present invention provides; The chemical conversionsolution for a metal structure wherein the compound (A) contains atleast one member selected from germanium nitrate, germanium sulfate,germanium fluoride, tin nitrate, tin sulfate, tin fluoride, coppernitrate, copper sulfate, and copper fluoride.

More preferably, the present invention provides; The chemical conversionsolution for a metal structure wherein the compound (B) contains atleast one member selected from titanium sulfate, titanium oxysulfate,titanium ammonium sulfate, titanium nitrate, titanium oxynitrate,titanium ammonium nitrate, fluorotitanic acid, fluorotitanate complex,zirconium sulfate, zirconium oxysulfate, zirconium ammonium sulfate,zirconium nitrate, zirconium oxynitrate, zirconium ammonium nitrate,fluorozirconic acid, and fluorozirconate complex.

More preferably, the present invention provides; The chemical conversionsolution for a metal structure wherein the compound (C) contains atleast one member selected from germanium nitrate, tin nitrate, coppernitrate, titanium nitrate, zirconium nitrate, magnesium nitrate, calciumnitrate, aluminum nitrate, zinc nitrate, strontium nitrate, andmanganese nitrate.

More preferably, the present invention provides; The chemical conversionsolution for a metal structure wherein the compound (D) contains atleast one member selected from aluminum nitrate, aluminum sulfate,aluminum fluoride, magnesium nitrate, magnesium sulfate, and magnesiumfluoride.

More preferably, the present invention provides; The chemical conversionsolution for a metal structure wherein the compound (E) contains atleast one member selected from zinc nitrate and zinc sulfate

More preferably, the present invention provides; The chemical conversionsolution for a metal structure wherein the compound (F) contains atleast one member selected from hydrofluoric acid, ammonium fluoride,germanium fluoride, tin fluoride, copper fluoride, fluorotitanic acid,fluorotitanate complex, fluorozirconic acid, fluorozirconate complex,aluminum fluoride and magnesium fluoride.

More preferably, the present invention provides; The chemical conversionsolution for a metal structure wherein the cationic water-soluble resin(G) contains at least one member selected from amino group-containingwater-soluble oligomer and water-soluble polymer, and content of theresin (G) is in the range of 0.001 mmol/L to 10 mmol/L.

More preferably, the present invention provides; The chemical conversionsolution for a metal structure wherein the coupling agent (H) containsat least one member selected from silicon-containing coupling agent andtitanium-containing coupling agent, and content of the coupling agent(H) is 0.001 mmol/L to 10 mmol/L.

More preferably, the present invention provides; The chemical conversionsolution for a metal structure wherein the chelating agent (I) containsat least one member selected from oxalic acid, tartaric acid, citricacid, malic acid, organic phosphonic acid, nitrilotriacetic acid (NTA),and ethylenediaminetetraacetic acid (EDTA).

More preferably, the present invention provides; The chemical conversionsolution for a metal structure wherein the metal structure is atransportation vehicle or its part constituted from at least one memberselected from cold rolled steel plate, aluminum or aluminum alloy plate,zinc or zinc alloy plate, galvanized steel plate, and galvannealed steelplate, and the chemical conversion solution also contains metal ionsdissolved from the metal structure.

Moreover, the present invention provides; A method for treating asurface of a metal structure comprising the steps of; —

conducting chemical conversion of the metal structure by using thechemical conversion solution for a metal structure to form a chemicalconversion film on the surface of the metal structure to a coatingweight in terms of at least one member selected from germanium, tin, andcopper of 0.01 mmol/m² to 1 mmol/m², and in terms of at least one memberselected from titanium and zirconium of 0.02 mmol/m² to 2 mmol/m², and 2to 200 nm in terms of thickness of the film

rinsing the metal structure with water, and then, with deionized water,and without drying,

subjecting the surface of the metal structure to electrodeposition.

The chemical conversion solution and the surface treating method for ametal structure of the present invention are capable of realizing highcorrosion resistance as well as high coating adhesion of the metalsurface without using the harmful hexavalent chromium. The chemicalconversion solution and the surface treating method for a metalstructure of the present invention are also capable of realizing highthrowing power during electrodeposition on a complicated structure as inthe case of, for example, a transportation vehicle, namely, anautomobile. The chemical conversion solution and the surface treatmentand the surface treating method of the present invention are alsocapable of controlling and reducing the industrial wastes such as sludgein the commercial scale production.

DETAILED DESCRIPTION OF THE INVENTION

First, various components constituting the chemical conversion solutionof the present invention are described.

Compounds (A) to (F)

The at least one compound (A) selected from water-soluble germaniumcompound, water-soluble tin compound, and water-soluble copper compoundis an essential component, and this component greatly contributes forthe improvement of throwing power in the electrodeposition. The at leastone compound selected from water-soluble germanium compound,water-soluble tin compound, and water-soluble copper compound preferablycomprises at least one member selected from germanium nitrate, germaniumsulfate, germanium fluoride, tin nitrate, tin sulfate (II), tin (IV)nitrate, tin fluoride, copper nitrate, copper sulfate, and copperfluoride, and more preferably, at least one member selected fromgermanium fluoride, tin fluoride, tin (II) nitrate, and copper nitrate.

Content (C_(A)) of the compound (A) is preferably in the range of 0.05mmol/L to 10 mmol/L, and more preferably 0.1 mmol/L to 1 mmol/L in termsof the total metal content of each compound. When the content (C_(A)) isless than 0.05 mmol/L, concentration of the compound (A) in the chemicalconversion solution will be insufficient, and coating weight of thecompound (A) will be insufficient. When the content (C_(A)) is in excessof 10 mmol/L, concentration in the chemical conversion solution will behigh, and the increased cost is economically unfavorable.

The at least one compound (B) selected from water-soluble titaniumcompound and water-soluble zirconium compound is also an essentialcomponent, and this component greatly contributes for the improvement ofcorrosion resistance. The compound (B) preferably contains at least onecompound selected from titanium sulfate, titanium oxysulfate, titaniumammonium sulfate, titanium nitrate, titanium oxynitrate, titaniumammonium nitrate, fluorotitanic acid, fluorotitanate complex, zirconiumsulfate, zirconium oxysulfate, zirconium ammonium sulfate, zirconiumnitrate, zirconium oxynitrate, zirconium ammonium nitrate,fluorozirconic acid, and fluorozirconate complex, and more preferably,at least one compound selected from fluorotitanic acid, zirconiumnitrate, and fluorozirconic acid. Content (C_(B)) of the compound (B) ispreferably in the range of 0.1 mmol/L to 10 mmol/L, and more preferably0.5 mmol/L to 5 mmol/L in terms of the total of the titanium and/or thezirconium. When the content (C_(B)) is less than 0.1 mmol/L,concentration in the chemical conversion solution will be insufficient,and coating weight of the compound (B) will be insufficient. When thecontent (C_(B)) is in excess of 10 mmol/L, concentration in the chemicalconversion solution will be high, and the increased cost is economicallyunfavorable.

The water-soluble nitrate compound (C) is also an essential component,and this component has influence on the uniformity of the resultingchemical conversion film and greatly contributes for the improvement offinal corrosion resistance. Presumably, the compound (C) suppressesexcessive etching at the interface between the chemical conversionsolution and the metal during the chemical conversion, and thiscontributes for the improvement in the uniformity of the chemicalconversion film. The compound (C) is preferably at least one compoundselected from germanium nitrate, tin nitrate, copper nitrate, titaniumnitrate, zirconium nitrate, magnesium nitrate, calcium nitrate, aluminumnitrate, zinc nitrate, strontium nitrate, and manganese nitrate, andmore preferably at least one compound selected from tin nitrate,zirconium nitrate, magnesium nitrate, aluminum nitrate, and zincnitrate. Content (C_(C)) of the nitrate compound (C) is preferably inthe range of 3 mmol/L to 300 mmol/L, and more preferably 20 mmol/L to200 mmol/L in terms of the nitrate radical from the nitrate salt. Whenthe content (C_(C)) is less than 3 mmol/L, uniformity of the chemicalconversion film will be insufficient, and the final corrosion resistancewill be insufficient. Content (C_(C)) in excess of 300 mmol/L does notadversely affect the improvement in the corrosion resistance. However,such high content inevitably results in the high nitrate radicalconcentration in the water used in the rinsing, and hence, in theincreased nitrogen content of the final waste water treatment, which mayinvite eutrophication.

The compound (D) selected from water-soluble aluminum compound andwater-soluble magnesium compound is also an essential component, and bysuppressing excessive etching, this component has the effect offacilitating efficient and uniform deposition of the chemical conversionfilm. The compound (D) is preferably at least one compound selected fromaluminum nitrate, aluminum sulfate, aluminum fluoride, magnesiumnitrate, magnesium sulfate, and magnesium fluoride, and more preferably,at least one compound selected from aluminum nitrate, aluminum sulfate,aluminum fluoride, magnesium nitrate, and magnesium sulfate.

Content (C_(D)) of the compound (D) is preferably in the range of 1mmol/L to 200 mmol/L, and more preferably 5 mmol/L to 50 mmol/L in termsof the total of the aluminum and/or the magnesium. When the content(C_(D)) is less than 1 mmol/L, efficient and uniform formation of thechemical conversion film is not realized, and this also results in theincrease of the time required for the film formation. Content (C_(D)) inexcess of 200 mmol/L does not adversely affect on the improvement in thecorrosion resistance. However, the high concentration in the chemicalconversion solution will invite increase in the cost which iseconomically unfavorable.

The water-soluble zinc compound (E) is also an essential component, andthis component has the effect of improving the uniformity of thechemical conversion film formed. The compound (E) preferably containszinc nitrate or zinc sulfate. Content (C_(E)) of the compound (E) ispreferably in the range of 0.2 mmol/L to 20 mmol/L, and more preferably1 mmol/L to 5 mmol/L in terms of the zinc. When the content (C_(E)) isless than 0.2 mmol/L, uniformity of the resulting chemical conversionfilm will not be sufficient, and as a consequence, the corrosionresistance will be insufficient. The content (C_(E)) in excess of 20mmol/L is not preferable since formation of the chemical conversion filmis likely to be prevented at such content.

The fluorine compound (F) is also an essential component, and is veryimportant. The fluorine compound (F) is a compound which has influenceon the etching of the metal, and in the case of the chemical conversionsolution of the present invention, the fluorine compound (F) has beenfound to also have a great effect on the corrosion resistance. It hasalso been found that generation of sludge in continuous operation of thechemical conversion can be suppressed by controlling the content of thefluorine compound (F) to specified range. In the prior art, stress hasbeen laid on the influence of the fluorine compound on the metaletching, and only very few documents have referred to the improvement ofthe corrosion resistance or stability of the chemical conversionsolution. The fluorine compound (F) preferably contains at least onecompound selected from hydrofluoric acid, ammonium fluoride, germaniumfluoride, tin fluoride, copper fluoride, fluorotitanic acid,fluorotitanate complex, fluorozirconic acid, fluorozirconate complex,aluminum fluoride, and magnesium fluoride.

Content of the fluorine compound (F) is closely related with the contentof the at least one compound (A) selected from water-soluble germaniumcompound, water-soluble tin compound, and water-soluble copper compound,the at least one compound (B) selected from water-soluble titaniumcompound and water-soluble zirconium compound, and the at least onecompound (D) selected from water-soluble aluminum and water-solublemagnesium compound. Based on the experimental findings, the content ofthe fluorine compound (F) is preferably in the range defined by thefollowing equations, namely, in the range determined by the contents ofthe compounds (A), (B), and (D).

Stable fluoride is formed when the compound (A) is divalent totetravalent, the compound (B) is hexavalent, and the compound (D) istrivalent when it is an aluminum compound and divalent when it is amagnesium compound. When the fluorine compound (F) is excessive, thecompound is believed to be in the form of HF. While stability of thechemical conversion solution is improved in the excess of the fluorinecompound (F), the chemical conversion film is not formed at excessivelyhigh concentration of the fluorine compound (F). In the meanwhile,excessively low concentration of the fluorine compound (F), the compoundwill result in the insufficient etching ability, and will result in thepartial surface etching (presumably due to the selective etching of therelatively active surface part). This results in the poor uniformity ofthe chemical conversion film, and hence, in the poor corrosionresistance. Stability of the chemical conversion solution will also beinsufficient, and this will result in the generation of the sludge. Thefollowing equations were determined by taking all of these findings inconsideration.

C _(F) (minimum value)=C _(A)×2+C _(B)×4+C _(D)×2

C _(F) (maximum value)=C _(A)×4+C _(B)×7+C _(D)×4

When the C_(F) is less than the C_(F) (minimum value) defined by theequation, etching ability of the chemical conversion solution will beinsufficient, and this will result in the partial surface etching(presumably due to the selective etching of the relatively activesurface part). This results in the formation of the chemical conversionfilm with poor uniformity, and hence, in the poor corrosion resistance.Stability of the chemical conversion solution will also be insufficient,and this will result in the increased sludge generation. On the otherhand, the C_(F) in excess of the C_(F) (maximum value) is not preferablesince excessively strong etching ability will result in the reducedefficiency of the chemical conversion film deposition. The morepreferable ranges of the C_(F) (optimal minimum value) and C_(F)(optimal maximum value) are as defined by the following equations.

C _(F) (optimal minimum value)=C _(A)×2+C _(B)×6+C _(D)×2

C _(F) (optimal maximum value)=C _(A)×3+C _(B)×6+C _(D)×4

pH of the Chemical Conversion Solution

In the chemical conversion solution of the present invention, pH is veryimportant, and the pH should be controlled to the range of 2.5 to 4.4.More specifically, intended merits of the chemical conversion solutionof the present invention are sufficiently realized only aftercontrolling the pH of the chemical conversion solution to the range of2.5 to 4.4 not only before its use in the chemical conversion but alsoduring the continuous operation of the chemical conversion. Accordingly,in the present invention, pH range has been limited to such range byalso considering the pH during the chemical conversion. When the pH isless than 2.5, the solution will have excessive etching ability, and thechemical conversion film will be deposited at an insufficientefficiency. On the other hand, the pH in excess of 4.4 will result inthe excessive sludge generation during the continuous chemicalconversion operation. More preferably, the pH is in the range of 3.0 to4.0. More specifically, the pH is preferably in somewhat lower range of3.0 to 3.6 when the compound (B) is a water-soluble titanium compound,and in somewhat high range of 3.4 to 4.0 when the compound (B) is awater-soluble zirconium compound. The method used for controlling the pHis not particularly limited, and the pH may be controlled by adding aninorganic acid such as nitric acid (which corresponds to the compound(C)) or hydrofluoric acid (which corresponds to the compound (F)), or byadding an organic acid such as oxalic acid, or alternatively, by addinga base such as ammonium hydrogen carbonate or ammonia solution.

Components (G) to (I)

Preferably, the chemical conversion solution for a metal structure ofthe present invention further comprises a cationic water-soluble resin(G). The water-soluble resin (G) has the merit that it improves thecoating adhesion by depositing simultaneously with other essentialcomponents to form the chemical conversion film. Incorporation of thecationic water-soluble resin (G) is particularly effective, for example,when the paint for electrodeposition coated over the chemical conversionfilm has poor adhesion. The water-soluble resin (G) preferably containsat least one member selected from amino group-containing water-solubleoligomer and water-soluble polymer. More specifically, the cationicwater-soluble resin (G) is preferably an amino group-containing oligomerwith the molecular weight of 2000 to 10000 or an amino group-containingpolymer with the molecular weight of 10000 to 30000 such as polyvinyl,polyvinyl phenol, or phenol formalin condensate oligomer or polymer. Inview of preventing the inhibition of the chemical conversion, thecationic water-soluble resin (G) is preferably an oligomer with lowermolecular weight. Content of the water-soluble resin (G) is in the rangeof 0.001 mmol/L to 10 mmol/L. This range may differ by the molecularweight of the cationic water-soluble resin (G) and when defined in termsof ppm by weight, the content is preferably in the range of 2 ppm to100,000 ppm, and more preferably 10 ppm to 400 ppm. Use of the cationicwater-soluble resin (G) at an excessively low content is meaninglesssince improvement in the coating adhesion is not realized at suchcontent. Excessively high content is also unpreferable in view ofeconomy, and also in view of the risk of inhibiting the chemicalconversion reaction.

Preferably, the chemical conversion solution for a metal structure ofthe present invention further comprises a coupling agent (H). Thecoupling agent (H) has the merit that it improves the coating a adhesionthrough deposition simultaneously with other essential components toform the chemical conversion film. Incorporation of the coupling agent(H) is particularly effective, for example, when the paint forelectrodeposition coated over the chemical conversion film has pooradhesion. The coupling agent (H) preferably contains at least one memberselected from silane coupling agent and titanium coupling agent. Morespecifically, the coupling agent (H) is preferably an aminogroup-containing aminosilane coupling agent or an epoxy group-containingepoxy silane coupling agent. Content of the coupling agent (H) ispreferably in the range of 0.001 mmol/L to 10 mmol/L, and morepreferably 0.1 mmol/L to 0.6 mmol/L. Use of the coupling agent (H) at anexcessively low content is meaningless since improvement in the coatingadhesion is not realized at such content. Excessively high content isalso unpreferable in view of economy, and also in view of the risk ofinhibiting the chemical conversion reaction.

Preferably, the chemical conversion solution for a metal structure ofthe present invention further comprises a metal chelating agent (I). Themetal chelating agent (I) has the merit that it improves the stabilityof the chemical conversion solution without forming the chemicalconversion film by depositing simultaneously with other essentialcomponents to form the chemical conversion film. When a large amount ofsolution is carried from the previous step (degreasing) and the like tothe step of the chemical conversion (for example, as in the case whenthe rinsing with water or the amount of water used in such rinsing isinsufficient), the pH often increases and this increase in the pH oftenhas the adverse effects on the stability of the chemical conversionsolution, and in such as case, incorporation of the metal chelatingagent (I) has the merit of improving the stability of the chemicalconversion solution. The metal chelating agent (I) preferably containsat least one member selected from oxalic acid, tartaric acid, citricacid, malic acid, organic phosphonic acid, NTA, and EDTA. Content of themetal chelating agent (I) is preferably in the range of 0.001 mmol/L to10 mmol/L, and more preferably 0.1 mmol/L to 0.6 mmol/L. Use of themetal chelating agent (I) at an excessively low content is meaninglesssince improvement in the stability of the chemical conversion solutionis not realized at such content. Excessively high content is alsounpreferable in view of economy, and also in view of the risk ofinhibiting the chemical conversion reaction.

Preparation of the Chemical Conversion Solution

The chemical conversion solution for a metal structure of the presentinvention is prepared by adding various component compounds in thesolvent water in arbitrary order, and stirring the mixture.

Metal Structure

The metal structure to be contacted with the chemical conversionsolution of the present invention for its surface treatment is notparticularly limited. The metal structure, however, is preferably atransportation vehicle or its part constituted from at least one metalmaterial selected from cold rolled steel plate, aluminum or aluminumalloy plate, zinc or zinc alloy plate, zinc-plated steel plate, andgalvannealed steel plate, which are used in the art.

Surface Treating Method

The surface treatment of the metal structure according to the presentinvention is conducted by bringing the metal structure in contact withthe chemical conversion solution for a metal structure as describedabove. In this surface treatment, the surface of the metal structurewhich is contacted with the chemical conversion solution should beclean, and oil, dirt, and metal powder (caused by abrasion, molding, andthe like) should be removed beforehand. The method used for the cleaningis not particularly limited, and a typical method used for commercialcleaning is the cleaning with an alkaline. After cleaning the metalstructure with water and removing the alkali components and the likeused for the cleaning, the surface of the metal structure is brought incontact with the chemical conversion solution of the present invention.The chemical conversion is preferably conducted at a temperature of 25°C. to 60° C. for a reaction time of typically 2 seconds to 600 secondsalthough the reaction time may vary by the material constituting themetal structure, concentration of the chemical conversion solution, andtemperature of the chemical conversion. When the metal structure has acomplicated shape as in the case of the automobile body, the structureis immersed in the solution for contact with the solution typically for30 seconds to 120 seconds since replacement of the solution in theinterior of the pocket structure is needed. Spraying and other surfacetreating method may also be used as long as the solution replacement ispossible.

There is no problem if the chemical conversion solution of the presentinvention contains the metal ion dissolved from the metal structureduring the continuous surface treating operation. For example, in thesurface treatment of a metal structure comprising a cold rolled steelplate, iron ion gradually increases in the chemical conversion solution.However, problems such as sludge generation will not occur as long ascontent of the compound constituting the solution is controlled to therange as described above. In the case of normal automobile body, thechemical conversion solution is naturally carried away with the transferof the automobile body, and the metal ion dissolved from the automobilebody reaches constant value at a relatively low concentration of lessthan 100 ppm by weight. Preferably, the dissolved metal ion is activelyremoved from the system, for example, by centrifugation or filtrationusing various membranes. In the case of the surface treatment of a metalstructure comprising a zinc-plated steel plate or aluminum, thedissolved metal ion may constitute the essential components of thepresent invention, and the chemical conversion solution of the presentinvention can be used more efficiently. The surface treated metalstructure is rinsed with water, and then, with deionized water, andwithout drying, the metal structure is subjected to coating byelectrodeposition.

Chemical Conversion Film

By the surface treating method of the present invention, a film isformed so that coating weight of the chemical conversion film on thesurface of the metal structure is 0.01 mmol/m² to 1 mmol/m² in terms ofgermanium, tin, copper, or their total weight, and 0.02 mmol/m² to 2mmol/m² in terms of titanium, zirconium, or their total weight, or 2 nmto 200 nm in thickness. When the coating weight in terms of germanium,tin, copper, or their total weight is less than 0.01 mmol/m², throwingpower in the coating by electrodeposition is not sufficiently improved.On the other hand, the coating weight in excess of 1 mmol/m² has noparticular problem while excessive use of such expensive material iseconomically unfavorable. More preferably, the coating weight is in therange of 0.1 mmol/m² to 0.5 mmol/m². The preferable range, however, mayvary by the material constituting the metal structure, and a relativelyhigh coating weight is required in the case of the cold rolled steelplate. In the case of galvannealed steel plate a sufficient throwingpower is realized at a lower coating weight, and in the case of aluminummaterial, sufficient throwing power is realized at even lower coatingweight. It is to be considered that the germanium and/or tin and/orcopper is basically present in the form of oxide, hydroxide, orfluoride. Although the nature of the germanium, tin, and copper may besomewhat different by the type of the metal structure, they arebasically present as a conductor or semiconductor on the surface of themetal structure, and they adequately control the hydrogen gas generationduring the electrodeposition. They also improve adhesion between thefilm and the deposited coating, and as a consequence, they improveresistance of the electrodeposited components, and hence, throwing powerduring the electrodeposition. Accordingly, germanium, tin, or copper ispreferably present at the outermost surface of the film.

When the titanium, zirconium or their total weight is less than 0.02mmol/m², the coating weight is insufficient, and hence, the corrosionresistance is insufficient. On the other hand, a sufficient corrosionresistance is realized at a coating weight in excess of 2 mmol/m², whilesuch excessive coating weight is economically unfavorable due to theincreased surface treatment cost. More preferably, the coating weight isin the range of 0.1 mmol/m² to 1 mmol/m², and this corresponds to thethickness of 2 nm to 200 nm, and more preferably, 20 nm to 100 nm. It isto be noted that the titanium and/or zirconium is also postulated to bebasically present in the form of oxide or hydroxide. In principle,titanium and/or zirconium has high barrier properties with high acid andalkaline resistance, and this contributes for the high corrosionresistance. The film in terms of the thickness is in the range of 2 to200 nm, and a more preferable film has a thickness of 20 to 100 nm. Itis to be considered that this substance is also present in the form ofoxide or hydroxide, and in principle, it has high barrier propertieswith high acid and alkaline resistance, and this contributes for thehigh corrosion resistance.

EXAMPLES

Next, novelty, inventive step, and utility of the chemical conversionsolution and the surface treating method for a metal structure of thepresent invention are described in detail by referring to Examples andComparative Examples.

First, the metal plates, the surface treating method, the pretreatment(cleaning), and the electrodeposition of the metal plates are described.Composition of the chemical conversion solution and the test method(evaluation method) of the metal plates are then described. The resultsof the tests (evaluations) are summarized in Tables 1 to 3.

Metal Plate

Three metal plates, namely, a cold rolled steel plate [70×150×0.8 mm;SPCC (JIS 3141) manufactured by PALTEC], galvannealed steel plate[70×150×0.8 mm; SGCC F06 MO (JIS G3302) manufactured by PALTEC], andaluminum alloy plate [70×150×1.0 mm; A5052P (JIS 4000) manufactured byPALTEC] were used. In the following description, the cold rolled steelplate is abbreviated as SPC, the galvannealed steel plate is abbreviatedas GA, and the aluminum alloy plate is abbreviated as AL

Cleaning Method

The surface of each metal plate was degreased by using a degreaser [FineCleaner E2001 (component A, 13 g/l; component B, 7 g/l) manufactured byNihon Parkerizing Co., Ltd.]. More specifically, the degreaser was usedby heating the metal plate to 40° C. and spraying the degreaser for 120seconds. The metal plate was then rinsed by spraying water for 30seconds, and the surface of the metal plate was treated by using thechemical conversion solution to thereby form the chemical conversionfilm. The box as described below was treated by using the samedegreaser. However, the degreasing was conducted by dipping for 180seconds. The rinsing with water was also conducted by dipping for 60seconds with thorough shaking.

Surface Treating Method

The chemical conversion solution having the composition as will bedescribed later was prepared. The chemical conversion solution wasstirred at the predetermined temperature for 1 hour, and then allowed tostand to examine the stability of the pH and the like as well as thegeneration of precipitate (sludge generation). Then appearance of thechemical conversion solution was observed, and this appearance isreferred to as the initial appearance. The metal plate was then surfacetreated by one of the following surface treating methods (1) to (3).After the surface treatment, the metal plate was rinsed under runningtap water (at room temperature for 30 seconds), and then, with deionizedwater (at room temperature for 30 seconds).

Surface Treating Method (1)

Surface treating temperature: 45° C.

Surface treating time: 90 seconds

Contact method: dipping

Surface Treating Method (2)

Surface treating temperature: 35° C.

Surface treating time: 120 seconds

Contact method: dipping

Surface Treating Method (3)

Surface treating temperature: 50° C.

Surface treating time: 45 seconds

Contact method: dipping

Electrodeposition Method

The metal plate which had been formed with the chemical conversion filmand which had been rinsed with water and deionized water without dryingwas subjected to electrodeposition by using an electrodeposition paint[GT-10HT manufactured by Kansai Paint Co., Ltd.]. The cathodicelectrolysis was conducted at a constant voltage for 180 seconds todeposit the coating, and after rinsing with water, the coating was bakedat 170° C. for 20 minutes to thereby complete the coating byelectrodeposition. The coating thickness was adjusted to 20 μm bycontrolling the voltage.

Example 1

Chemical conversion solution 1 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box as described below was conducted by the surface treatingmethod (1) to form a chemical conversion film. The chemical conversionsolution 1 was prepared by adding the following components (A) to (F) to80% of the total content of water in the order of (F), (A), (B), (D),and (E), finally adding water to the predetermined volume, and stirringat room temperature for 20 minutes. The solution was heated to thepredetermined temperature, and pH was adjusted. The surface treatedmetal plate was rinsed with water, and then with deionized water, andwithout drying, the metal plate was subjected to the electrodepositionby using the procedure and conditions as described above to thereby formthe coating.

Chemical Conversion Solution 1

(A): tin fluoride, 0.2 mmol/L

(B): fluorotitanic acid, 3 mmol/L

(C): nitrate radical from (D) and (E), 10 mmol/L

(D): aluminum nitrate, 2 mmol/L

(E): zinc nitrate, 2 mmol/L

(F): total fluorine in hydrofluoric acid, (A), and (B), 23 mmol/L

pH adjusted to 3.2 with ammonia solution

C_(F) (minimum value) was calculated to be 16.4 mmol/L, and C_(F)(maximum value) was calculated to be 29.8 mmol/L.

Coating Weight of the Chemical Conversion Solution

Coating weight of the chemical conversion solution on the surfacetreated metal plate was measured by using X-ray fluorescence analyzer(System 3270E manufactured by Rigaku Corporation). For the measurementof the coating weight, the surface treated metal plate was used afterrinsing with water, and then with deionized water, and drying with coldair.

Thickness of the Chemical Conversion Film

Thickness of the chemical conversion film of the surface treated metalplate was measured by surface analyzer (ESCA-850M manufactured byShimadzu Corporation; used at a sputtering speed of 80 nm/minute). Morespecifically, the chemical conversion film was sputtered with argon, andthe time required until the percentage of the matrix metal reached 70%by atom was measured, and the film thickness was calculated from thissputtering time. The metal plate used for the measurement was the oneused for the measurement of the coating weight.

Coating Adhesion

Cross cuts were made on the metal plate having the electrodepositedcoating, and after immersing the metal plate in boiling water for 1hour, water was wiped off the metal plate. An adhesive tape was attachedand peeled to observe the state of the metal plate with the cross cuts.Of the 100 squares formed by the cross cuts, the squares remaining onthe metal plate without being peeled off the plate was counted.Accordingly, 100 is the best and 0 is the worst.

Thickness of the Electrodeposited Coating

Coating thickness of the metal plate after the coating by theelectrodeposition was measured by using a commercially availableelectromagnetic coating thickness tester (LZ-200 manufactured by KettElectric Laboratory).

Corrosion Resistance

Salt spray test (JIS-Z2371) was conducted after forming cross cuts onthe electrodeposited metal plate, and single side bulging width wasevaluated after 1000 hours. In general, in the case of a cold rolledsteel plate, the corrosion resistance is evaluated “good” when thesingle side blister width is up to 3 mm and “excellent” when the singleside blister width is up to 2 mm. In the case of a galvannealed steelplate, the corrosion resistance is evaluated “good” when the single sideblister width is up to 1.2 mm, and up to 0.5 mm in the case of analuminum alloy plate.

Test Method for Evaluating Throwing Power in the Coating byElectrodeposition

4 metal plates 12, 13, 14, and 15 of the same type were prepared, and ahole 10 having a diameter of 8 mm was formed in 3 (12, 13, and 14) ofthe 4 plates at a position 50 mm from the bottom and at the samedistance from both sides. The 4 metal plates 12 to 15 were assembled asshown in FIG. 1 with the metal plates arranged at an interval of 20 mm.Vinyl chloride plates 21, 22, and 23 were attached to both sides andbottom of the metal plates 12 to 15, and the vinyl chloride plates 21 to23 and the metal plate 12 to 15 were fixedly secured by using anadhesive tape to thereby complete the assembly of four-plate box 1. Thethus assembled box was subjected to surface treatment, and withoutdrying, this surface treated box was coated by electrodeposition. Astainless steel (SUS304) plate having a size of 70 mm×150 mm×0.55 mmhaving one surface insulated with an insulator tape was used for thecounter electrode. The coating composition for the electrodeposition wasfilled until the metal plates 12 to 15 and the counter electrode wereimmersed to a depth of 90 mm. The coating composition for theelectrodeposition was maintained at a temperature of 28° C., and theelectrodeposition was conducted while stirring the composition with astirrer. Wiring was conducted to short-circuit all of the 4 metal plates12 to 15, and a coating was deposited by cathodic electrolysis using thecounter electrode for the anode by using a rectifier. More specifically,the electrolysis was conducted by linearly increasing the voltage to theanode from 0 V to 230 V in 30 seconds, and maintaining the voltage at230 V for 150 seconds. After the electrolysis, the metal plates 12 to 15were rinsed with water, and baked at 170° C. for 20 minutes to form thecoating. The surface on the side of the counter electrode of the metalplate 12 nearest to the counter electrode was designated “surface A”,and the surface on the side of the counter electrode of the metal plate15 which is the plate most remote from the counter electrode wasdesignated “surface G”. Coating thickness of the surface A and thesurface G was measured, and the A/G ratio was used as an index of thethrowing power in the coating by electrodeposition. In general, theratio of up to 2.5 is the acceptable level, and the ratio of up to 2.0is the excellent level.

Sludge Generation Test

Sludge generation test was conducted in order to evaluate feasibilityfor commercial scale production of the surface treatment. First, initialappearance of the chemical conversion solution was checked. Next, themetal plates as described above were continuously surface treated byusing 1 L of the chemical conversion solution for 10 minutes. Loss ofthe solution in the surface treatment caused by the formation of thechemical conversion film and carrying over to the subsequent step wasadequately replenished to keep the initial level. The chemicalconversion solution after the surface treatment was allowed to stand at40° C. for 48 hours, and the chemical conversion solution was visuallyevaluated for its state (such as turbidity) and generation of theprecipitate (the sludge generation). The solution with no sludgegeneration is favorable.

Example 2

Chemical conversion solution 2 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (3). Thechemical conversion solution was prepared by adding the followingcomponents (A) to (F) to 80% of the total content of water in the orderof (F), (A), (B), (D), and (E), finally adding water to thepredetermined volume, and stirring at room temperature for 20 minutes.The solution was heated to the predetermined temperature, and pH wasadjusted. The surface treated metal plate was rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Chemical Conversion Solution 2

(A): tin fluoride, 1 mmol/L

(B): fluorotitanic acid, 5 mmol/L

(C): nitrate radical from (D) and (E), 40 mmol/L

(D): aluminum nitrate, 10 mmol/L

(E): zinc nitrate, 5 mmol/L

(F): total fluorine in hydrofluoric acid, (A), and (B), 47 mmol/L

pH adjusted to 3.6 with ammonia solution

C_(F) (minimum value) was calculated to be 42 mmol/L, and C_(F) (maximumvalue) was calculated to be 79 mmol/L.

Example 3

Chemical conversion solution 3 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (2). Thechemical conversion solution was prepared by adding the followingcomponents (A) to (F) to 80% of the total content of water in the orderof (F), (A), (B), (D), and (E), finally adding water to thepredetermined volume, and stirring at room temperature for 20 minutes.The solution was heated to the predetermined temperature, and pH wasadjusted. The surface treated metal plate was rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Chemical Conversion Solution 3

(A): germanium fluoride, 0.5 mmol/L

(B): fluorotitanic acid, 0.1 mmol/L; fluorozirconic acid, 0.5 mmol/L

(C): nitrate radical from (D) and (E), 8 mmol/L

(D): aluminum nitrate, 2 mmol/L

(E): zinc nitrate, 1 mmol/L

(F): total fluorine in hydrofluoric acid and (B), 10 mmol/L

pH adjusted to 3.7 with ammonia solution

C_(F) (minimum value) was calculated to be 7.4 mmol/L, and C_(F)(maximum value) was calculated to be 14.2 mmol/L.

Example 4

Chemical conversion solution 4 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (1). Thechemical conversion solution was prepared by adding the followingcomponents (A) to (F) to 80% of the total content of water in the orderof (F), (A), (B), (D), and (E), finally adding water to thepredetermined volume, and stirring at room temperature for 20 minutes.The solution was heated to the predetermined temperature, and pH wasadjusted. The surface treated metal plate was rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Chemical Conversion Solution 4

(A): tin (II) nitrate, 1 mmol/L

(B): fluorozirconic acid, 4 mmol/L

(C): nitrate radical from (A) and (E): 4 mmol/L

(D): magnesium sulfate, 10 mmol/L

(E): zinc nitrate, 1 mmol/L

(F): total fluorine in ammonium fluoride and (B), 47 mmol/L

pH adjusted to 4.4 with ammonia solution

C_(F) (minimum value) was calculated to be 38 mmol/L, and C_(F) (maximumvalue) was calculated to be 72 mmol/L.

Example 5

Chemical conversion solution 5 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (2). Thechemical conversion solution was prepared by adding the followingcomponents (A) to (F) to 80% of the total content of water in the orderof (F), (A), (B), (D), and (E), finally adding water to thepredetermined volume, and stirring at room temperature for 20 minutes.The solution was heated to the predetermined temperature, and pH wasadjusted. The surface treated metal plate was rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Chemical Conversion Solution 5

(A): tin fluoride, 0.2 mmol/L; germanium fluoride, 0.2 mmol/L

(B): zirconium nitrate, 4 mmol/L

(C): nitrate radical from (B), (D), and (E): 31 mmol/L

(D): aluminum nitrate, 5 mmol/L

(E): zinc nitrate, 4 mmol/L

(F): total fluorine in hydrofluoric acid and (A), 40 mmol/L

pH adjusted to 4.2 with ammonia solution

C_(F) (minimum value) was calculated to be 26.8 mmol/L, and C_(F)(maximum value) was calculated to be 49.6 mmol/L.

Example 6

Chemical conversion solution 6 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (1). Thechemical conversion solution was prepared by adding the followingcomponents (A) to (F) to 80% of the total content of water in the orderof (F), (A), (B), (D), and (E), finally adding water to thepredetermined volume, and stirring at room temperature for 20 minutes.The solution was heated to the predetermined temperature, and pH wasadjusted. The surface treated metal plate was rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Chemical Conversion Solution 6

(A): tin (II) nitrate, 0.5 mmol/L; germanium nitrate, 1 mmol/L

(B): fluorozirconic acid, 5 mmol/L

(C): nitrate radical from (A), (D), and (E), 34 mmol/L

(D): aluminum nitrate, 10 mmol/L

(E): zinc nitrate, 0.5 mmol/L

(F): total fluorine in hydrofluoric acid and (B), 60 mmol/L

pH adjusted to 3.8 with ammonia solution

C_(F) (minimum value) was calculated to be 43 mmol/L, and C_(F) (maximumvalue) was calculated to be 81 mmol/L.

Example 7

Chemical conversion solution 7 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (2). Thechemical conversion solution was prepared by adding the followingcomponents (A) to (F) to 80% of the total content of water in the orderof (F), (A), (B), (D), and (E), finally adding water to thepredetermined volume, and stirring at room temperature for 20 minutes.The solution was heated to the predetermined temperature, and pH wasadjusted. The surface treated metal plate was rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Chemical Conversion Solution 7

(A): tin fluoride, 1 mmol/L; germanium fluoride, 0.1 mmol/L

(B): fluorozirconic acid, 2 mmol/L

(C): nitrate radical from (E), 1 mmol/L

(D): magnesium fluoride, 0.6 mmol/L

(E): zinc nitrate, 0.5 mmol/L

(F): total fluorine in hydrofluoric acid, (A), (B), and (D), 17 mmol/L

pH adjusted to 4.0 with ammonia solution

C_(F) (minimum value) was calculated to be 11.4 mmol/L, and C_(F)(maximum value) was calculated to be 20.8 mmol/L.

Example 8

Chemical conversion solution 8 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (1). Thechemical conversion solution was prepared by adding the followingcomponents (A) to (G) to 80% of the total content of water in the orderof (F), (A), (B), (D), (E) and (G), finally adding water to thepredetermined volume, and stirring at room temperature for 20 minutes.The solution was heated to the predetermined temperature, and pH wasadjusted. The surface treated metal plate was rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Chemical Conversion Solution 8

(A): tin fluoride, 1 mmol/L; germanium fluoride, 0.1 mmol/L

(B): fluorozirconic acid, 2 mmol/L

(C): nitrate radical from (D) and (E): 11 mmol/L

(D): magnesium nitrate, 5 mmol/L

(E): zinc nitrate, 0.5 mmol/L

(F): total fluorine in hydrofluoric acid, (A), and (B), 22 mmol/L

(G): aminated polyvinyl phenol (average molecular weight, 10000), 0.004mmol/L

pH adjusted to 3.3 with ammonia solution

C_(F) (minimum value) was calculated to be 20.2 mmol/L, and C_(F)(maximum value) was calculated to be 38.8 mmol/L.

Example 9

Chemical conversion solution 9 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (3). Thechemical conversion solution was prepared by adding the followingcomponents (A) to (G) to 80% of the total content of water in the orderof (F), (A), (B), (D), (E) and (G), finally adding water to thepredetermined volume, and stirring at room temperature for 20 minutes.The solution was heated to the predetermined temperature, and pH wasadjusted. The surface treated metal plate was rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Chemical Conversion Solution 9

(A): tin fluoride, 0.2 mmol/L; germanium fluoride, 0.2 mmol/L

(B): zirconium nitrate, 4 mmol/L

(C): nitrate radical from (B) and (E): 16 mmol/L

(D): aluminum sulfate, 2 mmol/L; magnesium sulfate, 3 mmol/L

(E): zinc nitrate, 4 mmol/L

(F): total fluorine in hydrofluoric acid and (A), 40 mmol/L

(G): condensation product of aminated phenol formalin (average molecularweight, 2000), 0.1 mmol/L

pH adjusted to 3.6 with ammonia solution

C_(F) (minimum value) was calculated to be 26.8 mmol/L, and C_(F)(maximum value) was calculated to be 49.6 mmol/L.

Example 10

Chemical conversion solution 10 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (1). Thechemical conversion solution was prepared by adding the followingcomponents (A) to (F) to 80% of the total content of water in the orderof (F), (A), (B), nitric acid, (D), and (E), finally adding water to thepredetermined volume, and stirring at room temperature for 20 minutes.The solution was heated to the predetermined temperature, and pH wasadjusted. The surface treated metal plate was rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Chemical Conversion Solution 10

(A): tin (IV) nitrate, 0.2 mmol/L

(B): fluorozirconic acid, 2 mmol/L

(C): nitrate radical from nitric acid, (A), (D), and (E), 40 mmol/L

(D): magnesium nitrate, 5 mmol/L

(E): zinc nitrate, 5 mmol/L

(F): total fluorine in ammonium fluoride and (B), 30 mmol/L

pH adjusted to 3.8 with ammonia solution

C_(F) (minimum value) was calculated to be 18.4 mmol/L, C_(F) (maximumvalue) was calculate 1 to be 34.8 mmol/L.

Example 11

Chemical conversion solution 11 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (1). Thechemical conversion solution was prepared by adding the followingcomponents (A) to (F) to 80% of the total content of water in the orderof (F), (A), (B), (D), and (E), finally adding water to thepredetermined volume, and stirring at room temperature for 20 minutes.The solution was heated to the predetermined temperature, and pH wasadjusted. The surface treated metal plate was rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Chemical Conversion Solution 11

(A): tin fluoride, 0.1 mmol/L

(B): fluorozirconic acid, 5 mmol/L

(C): nitrate radical from (D), 1.5 mmol/L

(D): aluminum nitrate, 0.5 mmol/L

(E): zinc sulfate, 0.4 mmol/L

(F): total fluorine in hydrofluoric acid, (A), and (B), 32 mmol/L

pH adjusted to 3.8 with ammonia solution

C_(F) (minimum value) was calculated to be 21.2 mmol/L, and C_(F)(maximum value) was calculated to be 37.4 mmol/L.

Example 12

Chemical conversion solution 12 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (3). Thechemical conversion solution was prepared by adding the followingcomponents (A) to (I) to 80% of the total content of water in the orderof (F), (A), (B), (D), (E), (H), and (I), finally adding water to thepredetermined volume, and stirring at room temperature for 20 minutes.The solution was heated to the predetermined temperature, and pH wasadjusted. The surface treated metal plate was rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Chemical Conversion Solution 12

(A): tin (II) nitrate, 0.5 mmol/L; germanium nitrate, 1 mmol/L

(B): fluorozirconic acid, 4 mmol/L; fluorotitanic acid, 1 mmol/L

(C): nitrate radical from (A), (D), and (E), 34 mmol/L

(D): aluminum nitrate, 10 mmol/L

(E): zinc nitrate, 0.5 mmol/L

(F): total fluorine in hydrofluoric acid and (B), 60 mmol/L

(H): epoxy silane coupling agent (G0261 manufactured by Tokyo ChemicalIndustry Co., Ltd.), 0.1 mmol/L

(I): ethylenediaminetetraacetic acid, 0.01 mmol/L

pH adjusted to 3.6 with ammonia solution

C_(F) (minimum value) was calculated to be 43 mmol/L, and C_(F) (maximumvalue) was calculated to be 81 mmol/L.

Example 13

Chemical conversion solution 13 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (1). Thechemical conversion solution was prepared by adding the followingcomponents (A) to (I) to 80% of the total content of water in the orderof (F), (A), (B), nitric acid, (D), (E), (H), and (I), finally addingwater to the predetermined volume, and stirring at room temperature for20 minutes. The solution was heated to the predetermined temperature,and pH was adjusted. The surface treated metal plate was rinsed withwater, and then with deionized water, and without drying, the metalplate was subjected to the electrodeposition by using the procedure andconditions as described above to thereby form the coating.

Chemical Conversion Solution 13

(A): tin (II) nitrate, 0.5 mmol/L, germanium nitrate, 1 mmol/L

(B): fluorozirconic acid, 4 mmol/L, fluorotitanic acid, 1 mmol/L

(C): nitrate radical from nitric acid, (A), (D), and (E): 20 mmol/L

(D): aluminum nitrate, 2 mmol/L

(E): zinc nitrate, 0.5 mmol/L

(F): total fluorine in hydrofluoric acid and (B), 40 mmol/L

(H): aminosilane coupling agent (A0876 manufactured by Tokyo ChemicalIndustry Co., Ltd.), 0.1 mmol/L

(I): nitrilotriacetic acid, 0.1 mmol/L

pH adjusted to 4.0 with ammonia solution

C_(F) (minimum value) was calculated to be 27 mmol/L, and C_(F) (maximumvalue) was calculated to be 49 mmol/L.

Example 14

Chemical conversion solution 14 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (2). Thechemical conversion solution was prepared by adding the followingcomponents (A) to (F) to 80% of the total content of water in the orderof (F), (A), (B), (D), and (E), finally adding water to thepredetermined volume, and stirring at room temperature for 20 minutes.The solution was heated to the predetermined temperature, and pH wasadjusted. The surface treated metal plate was rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Chemical Conversion Solution 14

(A): copper nitrate, 1 mmol/L

(B): fluorozirconic acid, 4 mmol/L

(C): nitrate radical from (A) and (E), 4 mmol/L

(D): magnesium sulfate, 10 mmol/L

(E): zinc nitrate, 1 mmol/L

(F): total fluorine in ammonium fluoride and (B), 47 mmol/L

pH adjusted to 4.4 with ammonia solution

C_(F) (minimum value) was calculated to be 38 mmol/L, and C_(F) (maximumvalue) was calculated to be 72 mmol/L.

Example 15

Chemical conversion solution 15 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (2). Thechemical conversion solution was prepared by adding the followingcomponents (A) to (I) to 80% of the total content of water in the orderof (F), (A), (B), nitric acid, (D), (E), (H), and (I), finally addingwater to the predetermined volume, and stirring at room temperature for20 minutes. The solution was heated to the predetermined temperature,and pH was adjusted. The surface treated metal plate was rinsed withwater, and then with deionized water, and without dying, the metal platewas subjected to the electrodeposition by using the procedure andconditions as described above to thereby form the coating.

Chemical Conversion Solution 15

(A): tin (II) nitrate, 0.5 mmol/L, copper nitrate, 1 mmol/L

(B): fluorozirconic acid, 4 mmol/L; fluorotitanic acid, 1 mmol/L

(C): nitrate radical from nitric acid, (A), (D), and (E), 15 mmol/L

(D): aluminum nitrate, 2 mmol/L

(E): zinc nitrate, 0.5 mmol/L

(F): total fluorine in hydrofluoric acid and (B), 40 mmol/L

(H): aminosilane coupling agent (A0876 manufactured by Tokyo ChemicalIndustry Co., Ltd.), 0.1 mmol/L

(I): nitrilotriacetic acid, 0.1 mmol/L

pH adjusted to 4.0 with ammonia solution

C_(F) (minimum value) was calculated to be 27 mmol/L, and C_(F) (maximumvalue) was calculated to be 49 mmol/L.

Comparative Example 1

Chemical conversion solution 16 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (1) to form achemical conversion film. The chemical conversion solution was preparedby adding the following components (B) to (F) to 80% of the totalcontent of water in the order of (F), (B), (D), and (E), finally addingwater to the predetermined volume, and stirring at room temperature for20 minutes. The solution was heated to the predetermined temperature,and pH was adjusted. The surface treated metal plate was rinsed withwater, and then with deionized water, and without drying, the metalplate was subjected to the electrodeposition by using the procedure andconditions as described above to thereby form the coating.

Chemical Conversion Solution 16

(A): None

(B): fluorozirconic acid, 5 mmol/L

(C): nitrate radical from (D), 40.8 mmol/L

(D): magnesium nitrate, 20 mmol/L

(E): zinc sulfate, 0.4 mmol/L

(F): total fluorine (fluorine in (B)), 30 mmol/L

pH adjusted to 3.6 with ammonia solution

C_(F) (minimum value) was calculated to be 60 mmol/L, and C_(F) (maximumvalue) was calculated to be 115 mmol/L.

Comparative Example 2

Chemical conversion solution 16 having the following composition wasprepared, and surface treatment of the three types of the metal plateand the box was conducted by the surface treating method (1) to form achemical conversion film. The chemical conversion solution was preparedby adding the following components (B) to (E) to 80% of the totalcontent of water in the order of (B) and (E), finally adding water tothe predetermined volume, and stirring at room temperature for 20minutes. The solution was heated to the predetermined temperature, andpH was adjusted. The surface treated metal plate was rinsed with water,and then with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Chemical Conversion Solution 16

(A): None

(B): fluorotitanic acid, 1 mmol/L

(C): nitrate radical from (E), 10 mmol/L

(D): None

(E): zinc nitrate, 0.4 mmol/L

(F): total fluorine (fluorine in (B)), 10 mmol/L

pH adjusted to 2.3 with nitric acid

C_(F) (minimum value) was calculated to be 4 mmol/L, and C_(F) (maximumvalue) was calculated to be 7 mmol/L.

Comparative Example 3

2% aqueous solution of Alodine (registered trademark) 404 (anon-chromate chemical conversion solution corresponding to JP2004-083824 A) was used. The surface treatment of the three types of themetal plate and the box was conducted by spraying this solution on theirsurface at 40° C. for 30 seconds to thereby form a chemical conversionfilm. Next, the surface treated metal plates were rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Comparative Example 4

Chemical conversion solution 8 (corresponding to JP 2004-232047 A)comprising 2 g/l of hexacyanoferrate, 1 g/L of fluorotitanic acid, and 1g/l of cobalt nitrate was prepared, and the three types of the metalplates were immersed in this solution at 40° C. for 60 seconds to carryout the surface treatment to thereby form a chemical conversion film.Next, the surface treated metal plates were rinsed with water, and thenwith deionized water, and without drying, the metal plate was subjectedto the electrodeposition by using the procedure and conditions asdescribed above to thereby form the coating.

Comparative Example 5

A surface treating solution (corresponding to WO 03/074761 A1)containing (1) 1 mmol/L of titanium sulfate, (2) hydrofluoric acid ofthe amount corresponding to sixfold by mole of titanium sulfate, (3) 0.2mmol/L of calcium nitrate, (4) 0.2 mmol/L of aluminum nitrate, and (5)nitrate ion (added in terms of (3) and (4)) was prepared, and the pH wasadjusted to 3.8. The three types of the metal plates and the box wereimmersed in this solution at 40° C. for 60 seconds to carry out thesurface treatment to thereby form a chemical conversion film. Next, thesurface treated metal plates were rinsed with water, and then withdeionized water, and without drying, the metal plate was subjected tothe electrodeposition by using the procedure and conditions as describedabove to thereby form the coating.

Comparative Example 6

1000 ppm by weight of zirconium (added as fluorozirconic acid), 1000 ppmby weight of zinc (added as zinc nitrate), 500 ppm by weight ofmagnesium (added as magnesium nitrate), 100 ppm by weight of titanium(added as fluorotitanic acid), 3 ppm by weight of indium (added asindium nitrate), and 800 ppm by weight of nitroguanidine were added towater in this order, and the mixture was stirred at room temperature toprepare the chemical conversion solution. The pH was adjusted to 4.5with ammonia solution. The three types of the metal plates and the boxwere immersed in this solution at 40° C. for 60 seconds to carry out thesurface treatment to thereby form a chemical conversion film (thisprocess corresponds to Example 14 of JP 2004-218073 A). Next, thesurface treated metal plates were rinsed with water, and then withdeionized water, and without drying, the metal plate was subjected tothe electrodeposition by using the procedure and conditions as describedabove to thereby form the coating.

Comparative Example 7

200 ppm by weight of zirconium (added as fluorozirconic acid), 500 ppmby weight of zinc (added as zinc nitrate), 200 ppm by weight of silica(added as Snowtex N), and 200 ppm by weight of ammonium persulfate wereadded to water in this order, and the mixture was stirred at roomtemperature to prepare the chemical conversion solution. The pH wasadjusted to 4.0 with ammonia solution. The three types of the metalplates and the box were immersed in this solution at 40° C. for 60seconds to carry out the surface treatment to thereby form a chemicalconversion film (this process corresponds to Example 3 of JP 2004-218073A). Next, the surface treated metal plates were rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Comparative Example 8

500 ppm by weight of zirconium (added as fluorozirconic acid), 1000 ppmby weight of magnesium (added as magnesium nitrate), 500 ppm by weightof calcium (added as calcium nitrate), and 100 ppm by weight of sodiumchlorate were added to water in this order, and the mixture was stirredat room temperature to prepare the chemical conversion solution. The pHwas adjusted to 4.5 with ammonia solution. The three types of the metalplates and the box were immersed in this solution at 25° C. for 60seconds to carry out the surface treatment to thereby form a chemicalconversion film (this process corresponds to Example 10 of JP2004-218073 A). Next, the surface treated metal plates were rinsed withwater, and then with deionized water, and without drying, the metalplate was subjected to the electrodeposition by using the procedure andconditions as described above to thereby form the coating.

Comparative Example 9

The three types of the metal plates and the box were immersed in 5%aqueous solution of PALBOND (registered trademark) L3020 (a zincphosphate-based chemical conversion agent) at 35° C. for 120 seconds tocarry out the surface treatment to thereby form a chemical conversionfilm. Next, the surface treated metal plates were rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating.

Comparative Example 10

Zirconium (500 ppm by weight of 40% zirconic acid in terms of the metalelement), an additive for improving the coating adhesion (200 ppm byweight of 3-aminopropyltriethoxysilane (“KBE903” manufactured byShin-Etsu Chemical Co., Ltd.) in terms of the effective componentconcentration), and a stabilizer (200 ppm by weight of HIDA(hydroxyethyl iminodiacetic acid)) were added, and the pH was adjustedto 4 with sodium hydroxide to prepare the chemical conversion solution.The KBE903 used was prepared by adding 5 parts by weight of KBE903dropwise at a constant rate from a dropping funnel to a mixed solvent of45 parts by mass of deionized water and 50 parts by mass of ethanol (ata solvent temperature of 25° C.) for 60 minutes; allowing the mixture toreact in nitrogen atmosphere at 25° C. for 24 hours; and allowing theethanol to evaporate by reducing the pressure of the reaction mixture tothereby obtain hydrolytic polycondensation product (hereinafter referredto as “KBE903 polycondensate A”) of KBE903 with the effective componentconcentration of 5%. The resulting chemical conversion solution had anORP (oxidation-reduction potential) of 308 mV, and the ratio of thecontent of the zirconium element to the total content of the siliconelement in the aminosilane and/or its hydrolytic polycondensationproduct (i.e. Zr/Si ratio) was 20. The three types of the metal platesand the box were immersed in this solution at 40° C. for 60 seconds tocarry out the surface treatment to thereby form a chemical conversionfilm. Next, the surface treated metal plates were rinsed with water, andthen with deionized water, and without drying, the metal plate wassubjected to the electrodeposition by using the procedure and conditionsas described above to thereby form the coating. (This procedure wasconducted according to JP 2008-88553 A.)

Comparative Example 11

The chemical conversion solution was prepared by repeating the procedureof Comparative Example 10 except that the additive for improving thecoating adhesion used was N-2-(aminoethyl)-3-aminopropyltrimethoxysilane(“KBM603” manufactured by Shin-Etsu Chemical Co., Ltd.) at an effectivecomponent concentrate: of 200 ppm by weight and the stabilizer used was100 ppm by weight of aspartic acid, and the zirconium was used at 250ppm by weight in terms of the metal element. The KBM603 used was thehydrolytic polycondensation product of KBM603 prepared by conducting thehydrolytic polycondensation by the procedure similar to that ofComparative Example 10 except that KBM603 was used instead of the KBE903(hereinafter referred to as “KBM603 polycondensate”). The resultingchemical conversion solution had an ORP of 356 mV, and the Zr/Si ratiowas 10. Surface treatment was conducted under the same conditions asdescribed from the Comparative Example 11 to form the chemicalconversion film. Next, the surface treated metal plates and the box wererinsed with water, and then with deionized water, and without drying,the metal plate was subjected to the electrodeposition by using theprocedure and conditions as described above to thereby form the coating.(This procedure was conducted according to JP 2008-88553 A.)

Comparative Example 12

The coating was formed by electrodeposition after cleaning (degreasing)the metal plate without conducting the surface treatment.

The results for the tests and the evaluations of the chemical conversionfilms of Examples 1 to 15 and Comparative Examples 1 to 12 are shown inTables 1 to 3. Table 1 shows the results for the cold rolled steelplate, Table 2 shows the results for the galvannealed steel plate, andTable 3 shows the results for the aluminum alloy plate. For all metalplates, the prior art techniques were insufficient in the throwing powerduring the coating by the electrodeposition except for the case usingthe phosphate. In the sludge generation test, precipitates were noted inmany of the prior art techniques, and this would be a serious problem inthe operability (production efficiency) in commercial scale production.In contrast, the chemical conversion solution and the surface treatingmethod of the present invention have realized excellent throwing powerin the coating by the electrodeposition simultaneously with highcorrosion resistance and coating adhesion as well as favorableoperability.

TABLE 1 Cold rolled steel plate Chemical conversion filmElectrodeposition Coating performance Property of the chemical(A)Coating (B)Coating Thickness Thickness Corrosion conversion solutionweight weight Thickness (surface A) (surface B) Coating resistanceDuring the mmol/m² mmol/m² nm μm μm A/G adhesion mm Initial reaction E.1Sn: 0.1 Ti: 0.

60 21 9 2.3 100 2.2 Transparent Transparent E.2 Sn: 0.3 Ti: 1.0 70 20 92.2 100 2.1 Transparent Transparent E.3 Ge: 0.1 Ti: 0.2, Zr: 0.6 40 2010 2.0 100 1.9 Transparent Transparent E.4 Sn: 0.3 Zr: 0.9 80 20 10 2.0100 1.9 Transparent Transparent E.5 Sn: 0.1, Ge: 0.1 Zr: 0.8 70 20 9 2.2100 2.0 Transparent Transparent E.6 Sn: 0.3, Ge: 0.3 Zr: 0.7 60 20 102.0 100 2.1 Transparent Transparent E.7 Sn: 0.3, Ge: 0.1 Zr: 0.7 60 2010 2.0 100 2.0 Transparent Transparent E.8 Sn: 0.3, Ge: 0.1 Zr: 0.6 5020 10 2.0 100 1.8 Transparent Transparent E.9 Sn: 0.1, Ge: 0.1 Zr: 0.760 20 9 2.2 100 1.8 Transparent Transparent E.10 Sn: 0.2 Zr: 0.6 50 2010 2.0 100 2.0 Transparent Transparent E.11 Sn: 0.1 Zr: 0.6 40 20 11 1.8100 2.0 Transparent Transparent E.12 Sn: 0.2, Ge: 0.1 Ti: 0.2, Zr: 0.670 20 10 2.0 100 1.6 Transparent Transparent E.13 Sn: 0.2, Ge: 0.1 Ti:0.2, Zr: 0.7 80 20 11 1.8 100 1.6 Transparent Transparent E.14 Cu: 0.3Zr: 0.9 80 20 11 1.8 100 1.9 Transparent Transparent E.15 Sn: 0.2, Cu:0.1 Ti: 0.2, Zr: 0.7 80 20 11 1.8 100 1.6 Transparent Transparent C.E.1— Zr: 0.5 40 27 2 13.5 100 2.3 Transparent Transparent C.E.2 — Ti: 0.210 28 2 14.0 99 4.5 Transparent Transparent C.E.3 — Zr: 0.2 20 28 2 14.095 4.0 Transparent Turbid (white) C.E.4 — Ti: 0.2 20 29 1 29.0 90 4.5Transparent Turbid (white) C.E.5 — Ti: 0.5 40 26 2 13.0 100 2.0Transparent Transparent C.E.6 In: ND Ti: ND, Zr: 0.2 20 28 1 28.0 95 3.3Turbid Sludge C.E.7 — Zr: 0.2 20 27 1 27.0 99 3.0 Slight turbid Turbid(white) C.E.8 — Zr: 0.1 10 28 1 28.0 95 3.8 Turbid Sludge C.E.9 — — 200020 10 2.0 100 3.0 Transparent Sludge C.E.10 — Zr: 0.56 40 25 6 4.2 953.0 Turbid Sludge C.E.11 — Zr: 0.56 40 26 5 5.2 95 3.0 Turbid SludgeC.E.12 — — — 26 2 13.0 80 6.5 — —

indicates data missing or illegible when filed

TABLE 2 Galvannealed steel plate Chemical conversion filmElectrodeposition Coating performance Property of the chemical(A)Coating (B)Coating Thick- Thickness Thickness Corrosion conversionsolution weight weight ness (surface A) (surface B) Coating resistanceDuring the mmol/m² mmol/m² Nm μm μm A/G adhesion Mm Initial reaction E.1Sn: 0.1 Ti: 0.4 30 20 9 2.2 100 1.0 Transparent Transparent E.2 Sn: 0.2Ti: 0.5 40 20 9 2.2 100 0.9 Transparent Transparent E.3 Ge: 0.1 Ti: 0.1,Zr: 0.4 40 20 11 1.8 100 1.0 Transparent Transparent E.4 Sn: 0.2 Zr: 0.560 20 11 1.8 100 1.0 Transparent Transparent E.5 Sn: 0.1, Ge: 0.1 Zr:0.6 50 19 9 2.1 100 1.0 Transparent Transparent E.6 Sn: 0.2, Ge: 0.1 Zr:0.5 40 20 10 2.0 100 1.0 Transparent Transparent E.7 Sn: 0.2, Ge: 0.1Zr: 0.7 50 20 11 1.8 100 1.0 Transparent Transparent E.8 Sn: 0.3, Ge:0.1 Zr: 0.5 50 20 10 2.0 100 0.8 Transparent Transparent E.9 Sn: 0.1,Ge: 0.1 Zr: 0.5 40 20 10 2.0 100 0.8 Transparent Transparent E.10 Sn:0.1 Zr: 0.5 40 20 10 2.0 100 0.9 Transparent Transparent E.11 Sn: 0.1Zr: 0.4 30 20 11 1.8 100 0.9 Transparent Transparent E.12 Sn: 0.2, Ge:0.1 Ti: 0.1, Zr: 0.5 50 20 11 1.8 100 0.8 Transparent Transparent E.13Sn: 0.2, Ge: 0.1 Ti: 0.1, Zr: 0.5 50 20 11 1.8 100 0.7 TransparentTransparent E.14 Cu: 0.2 Zr: 0.8 50 20 11 1.8 100 0.8 TransparentTransparent E.15 Sn: 0.2, Cu: 0.1 Ti: 0.1, Zr: 0.5 50 20 11 1.8 100 0.7Transparent Transparent C.E.1 — Zr: 0.4 30 25 3 8.3 100 1.2 TransparentTransparent C.E.2 — Ti:: 0.1 5 25 2 12.5 99 2.0 Transparent TransparentC.E.3 — Zr: 0.2 10 24 3 8.0 96 2.0 Transparent Turbid (white) C.E.4 —Ti: 0.1 10 26 2 13.0 90 2.3 Transparent Turbid (white) C.E.5 — Ti: 0.320 23 2 11.5 100 1.1 Transparent Transparent C.E.6 In: ND Ti: ND, Zr:0.2 15 25 2 12.5 95 1.6 Turbid (white) Sludge C.E.7 — Zr: 0.1 15 26 213.0 100 1.4 Slightly turbid Turbid (white) C.E.8 — Zr: 0.1 10 26 2 13.096 1.4 Turbid (white) Sludge C.E.9 — — 3500 20 10 2.0 100 1.2Transparent Sludge C.E.10 — Zr: 0.5 35 24 6 4.0 100 1.1 Turbid (white)Sludge C.E.11 — Zr: 0.5 35 25 5 5.0 95 1.1 Turbid (white) Sludge C.E.12— — — 25 3 8.3 85 2.4 — —

TABLE 3 Aluminum plate Chemical conversion film ElectrodepositionCoating performance Property of the chemical (A)Coating (B)CoatingThickness Thickness Corrosion conversion solution weight weightThickness (surface A) (surface B) Coating resistance During the mmol/m²mmol/m² nm μm μm A/G adhesion Mm Initial reaction E.1 Sn: 0.1 Ti: 0.3 1520 10 2.0 100 0.3 Transparent Transparent E.2 Sn: 0.1 Ti: 0.4 20 20 102.0 100 0.3 Transparent Transparent E.3 Ge: 0.1 Ti: 0.1, Zr: 0.3 40 2011 1.8 100 0.2 Transparent Transparent E.4 Sn: 0.2 Zr: 0.4 40 20 11 1.8100 0.3 Transparent Transparent E.5 Sn: 0.1, Ge: 0.1 Zr: 0.4 40 19 101.9 100 0.2 Transparent Transparent E.6 Sn: 0.2, Ge: 0.1 Zr: 0.4 40 2010 2.0 100 0.3 Transparent Transparent E.7 Sn: 0.2, Ge: 0.1 Zr: 0.5 4020 10 2.0 100 0.3 Transparent Transparent E.8 Sn: 0.2, Ge: 0.1 Zr: 0.440 20 10 2.0 100 0.3 Transparent Transparent E.9 Sn: 0.1, Ge: 0.1 Zr:0.4 40 20 10 2.0 100 0.3 Transparent Transparent E.10 Sn: 0.1 Zr: 0.3 3020 10 2.0 100 0.3 Transparent Transparent E.11 Sn: 0.1 Zr: 0.3 20 20 111.8 100 0.3 Transparent Transparent E.12 Sn: 0.1, Ge: 0.1 Ti: 0.1, Zr:0.2 30 20 11 1.8 100 0.2 Transparent Transparent E.13 Sn: 0.1, Ge: 0.1Ti: 0.1, Zr: 0.3 40 20 11 1.8 100 0.2 Transparent Transparent E.14 Cu:0.1 Zr: 0.4 40 20 11 1.8 100 0.2 Transparent Transparent E.15 Sn: 0.1,Cu: 0.1 Ti: 0.1, Zr: 0.3 50 20 11 1.8 100 0.2 Transparent TransparentC.E.1 — Zr: 0.

20 24 5 4.8 100 0.9 Transparent Transparent C.E.2 — Ti:: 0.1 5 25 4 6.3100 1.0 Transparent Transparent C.E.3 — Zr: 0.1 10 24 5 4.8 100 0.9Transparent Turbid (white) C.E.4 — Ti: 0.1 10 26 4 6.5 100 0.8Transparent Turbid (white) C.E.5 — Zr: 0.2 20 23 5 4.6 100 0.3Transparent Transparent C.E.6 In: ND Ti: ND, Zr: 0.1 10 25 4 6.3 97 1.0Turbid (white) Sludge C.E.7 — Zr: 0.1 10 26 4 6.5 100 0.9 Slight turbidTurbid (white) C.E.8 — Zr: 0.1 10 26 4 6.5 98 0.9 Turbid (white) Turbid(white) C.E.9 — — 3500 20 11 1.8 100 0.5 Transparent Sludge C.E.10 — Zr:0.3 20 25 7 3.6 100 0.5 Turbid (white) Sludge C.E.11 — Zr: 0.3 20 26 64.3 100 0.4 Turbid (white) Sludge C.E.12 — — — 25 4 6.3 85 1.0 — — E.:Example, C.E.: Comparative example, ND: Not determined

indicates data missing or illegible when filed

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a schematic view showing the box (four metal plate-box test)used in evaluating the throwing power in the electrodeposition.

EXPLANATIONS OF LETTERS OR NUMERALS

-   1 box-   10 hole-   12 test plate (metal plate after the coating) No. 1 (outside:    Surface A)-   13 test plate (metal plate after the coating) No. 2-   14 test plate (metal plate after the coating) No. 3-   15 test plate (metal plate after the coating) No. 4 (inside: Surface    G)-   21 side plate-   22 side plate-   23 bottom plate

1. A chemical conversion solution for a metal structure comprising (A)at least one compound selected from water-soluble germanium compound,water-soluble tin compound, and water-soluble copper compound (B) atleast one compound selected from water-soluble titanium compound andwater-soluble zirconium compound, (C) at least one water-soluble nitratecompound, (D) at least one compound selected from water-soluble aluminumcompound and water-soluble magnesium compound, (E) at least onewater-soluble zinc compound, and (F) at least one fluorine compound,wherein content (C_(A)) of at least one member selected from germanium,tin, and copper is 0.05 mmol/L to 10 mmol/L, content (C_(B)) of titaniumand/or zirconium is 0.1 mmol/L to 10 mmol/L, content (C_(C)) of nitrateradical in the water-soluble nitrate compound (C) is 3 mmol/L to 300mmol/L, content (C_(D)) of aluminum and/or magnesium is 1 mmol/L to 200mmol/L, content (C_(E)) of zinc is 0.2 mmol/L to 20 mmol/L, content(C_(F)) of fluorine in the fluorine compound (F) satisfies the followingequations:C _(F) (minimum value)=C _(A)×2+C _(B)×4+C _(D)×2C _(F) (maximum value)=C _(A)×4+C _(B)×7+C _(D)×4, and pH of thechemical conversion solution has been adjusted to the range of 2.5 to4.4. 2-15. (canceled)